diff --git a/core/.eslintrc.json b/core/.eslintrc.json
index 6a6916b1a2c0aef4d1f49b21c18bf21c423f067b..7b1ed46abeca6b8ae943e070edf3cd77e47a8b29 100644
--- a/core/.eslintrc.json
+++ b/core/.eslintrc.json
@@ -21,6 +21,7 @@
     "_": true,
     "Cookies": true,
     "Backbone": true,
+    "htmx": true,
     "loadjs": true,
     "Shepherd": true,
     "Sortable": true,
diff --git a/core/.phpstan-baseline.php b/core/.phpstan-baseline.php
index 6f4a52139f114e96d79dffef704a5acfa579831b..f50467a4dda42a068ac3c2831c2cf738c3641149 100644
--- a/core/.phpstan-baseline.php
+++ b/core/.phpstan-baseline.php
@@ -10443,12 +10443,6 @@
 	'count' => 1,
 	'path' => __DIR__ . '/lib/Drupal/Core/Template/Attribute.php',
 ];
-$ignoreErrors[] = [
-	'message' => '#^Method Drupal\\\\Core\\\\Template\\\\Attribute\\:\\:storage\\(\\) has no return type specified\\.$#',
-	'identifier' => 'missingType.return',
-	'count' => 1,
-	'path' => __DIR__ . '/lib/Drupal/Core/Template/Attribute.php',
-];
 $ignoreErrors[] = [
 	'message' => '#^Method Drupal\\\\Core\\\\Template\\\\AttributeArray\\:\\:getIterator\\(\\) return type with generic class ArrayIterator does not specify its types\\: TKey, TValue$#',
 	'identifier' => 'missingType.generics',
@@ -10461,6 +10455,12 @@
 	'count' => 1,
 	'path' => __DIR__ . '/lib/Drupal/Core/Template/AttributeValueBase.php',
 ];
+$ignoreErrors[] = [
+	'message' => '#^Method Drupal\\\\Core\\\\Template\\\\HtmxAttribute\\:\\:getIterator\\(\\) return type with generic class ArrayIterator does not specify its types\\: TKey, TValue$#',
+	'identifier' => 'missingType.generics',
+	'count' => 1,
+	'path' => __DIR__ . '/lib/Drupal/Core/Template/HtmxAttribute.php',
+];
 $ignoreErrors[] = [
 	'message' => '#^Constructor of class Drupal\\\\Core\\\\Template\\\\TwigEnvironment has an unused parameter \\$root\\.$#',
 	'identifier' => 'constructor.unusedParameter',
@@ -13761,30 +13761,12 @@
 	'count' => 1,
 	'path' => __DIR__ . '/modules/config/src/Form/ConfigSingleExportForm.php',
 ];
-$ignoreErrors[] = [
-	'message' => '#^Method Drupal\\\\config\\\\Form\\\\ConfigSingleExportForm\\:\\:findConfiguration\\(\\) has no return type specified\\.$#',
-	'identifier' => 'missingType.return',
-	'count' => 1,
-	'path' => __DIR__ . '/modules/config/src/Form/ConfigSingleExportForm.php',
-];
 $ignoreErrors[] = [
 	'message' => '#^Method Drupal\\\\config\\\\Form\\\\ConfigSingleExportForm\\:\\:submitForm\\(\\) has no return type specified\\.$#',
 	'identifier' => 'missingType.return',
 	'count' => 1,
 	'path' => __DIR__ . '/modules/config/src/Form/ConfigSingleExportForm.php',
 ];
-$ignoreErrors[] = [
-	'message' => '#^Method Drupal\\\\config\\\\Form\\\\ConfigSingleExportForm\\:\\:updateConfigurationType\\(\\) has no return type specified\\.$#',
-	'identifier' => 'missingType.return',
-	'count' => 1,
-	'path' => __DIR__ . '/modules/config/src/Form/ConfigSingleExportForm.php',
-];
-$ignoreErrors[] = [
-	'message' => '#^Method Drupal\\\\config\\\\Form\\\\ConfigSingleExportForm\\:\\:updateExport\\(\\) has no return type specified\\.$#',
-	'identifier' => 'missingType.return',
-	'count' => 1,
-	'path' => __DIR__ . '/modules/config/src/Form/ConfigSingleExportForm.php',
-];
 $ignoreErrors[] = [
 	'message' => '#^Method Drupal\\\\config\\\\Form\\\\ConfigSingleImportForm\\:\\:create\\(\\) has no return type specified\\.$#',
 	'identifier' => 'missingType.return',
diff --git a/core/assets/vendor/htmx/debug.js b/core/assets/vendor/htmx/debug.js
new file mode 100644
index 0000000000000000000000000000000000000000..15378ccc077720b1c91c05cf4bfd230fd3853f10
--- /dev/null
+++ b/core/assets/vendor/htmx/debug.js
@@ -0,0 +1,11 @@
+htmx.defineExtension('debug', {
+  onEvent: function(name, evt) {
+    if (console.debug) {
+      console.debug(name, evt)
+    } else if (console) {
+      console.log('DEBUG:', name, evt)
+    } else {
+      throw new Error('NO CONSOLE SUPPORTED')
+    }
+  }
+})
diff --git a/core/assets/vendor/htmx/htmx.min.js b/core/assets/vendor/htmx/htmx.min.js
new file mode 100644
index 0000000000000000000000000000000000000000..59937d712d905c314d0bbcd3c49cc8a15d0b6cdd
--- /dev/null
+++ b/core/assets/vendor/htmx/htmx.min.js
@@ -0,0 +1 @@
+var htmx=function(){"use strict";const Q={onLoad:null,process:null,on:null,off:null,trigger:null,ajax:null,find:null,findAll:null,closest:null,values:function(e,t){const n=cn(e,t||"post");return n.values},remove:null,addClass:null,removeClass:null,toggleClass:null,takeClass:null,swap:null,defineExtension:null,removeExtension:null,logAll:null,logNone:null,logger:null,config:{historyEnabled:true,historyCacheSize:10,refreshOnHistoryMiss:false,defaultSwapStyle:"innerHTML",defaultSwapDelay:0,defaultSettleDelay:20,includeIndicatorStyles:true,indicatorClass:"htmx-indicator",requestClass:"htmx-request",addedClass:"htmx-added",settlingClass:"htmx-settling",swappingClass:"htmx-swapping",allowEval:true,allowScriptTags:true,inlineScriptNonce:"",inlineStyleNonce:"",attributesToSettle:["class","style","width","height"],withCredentials:false,timeout:0,wsReconnectDelay:"full-jitter",wsBinaryType:"blob",disableSelector:"[hx-disable], 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t.path}Rn("get",e,t).then(function(){$t(e)});return}const n=R(s,/HX-Refresh:/i)&&s.getResponseHeader("HX-Refresh")==="true";if(R(s,/HX-Redirect:/i)){i.keepIndicators=true;location.href=s.getResponseHeader("HX-Redirect");n&&location.reload();return}if(n){i.keepIndicators=true;location.reload();return}if(R(s,/HX-Retarget:/i)){if(s.getResponseHeader("HX-Retarget")==="this"){i.target=o}else{i.target=ue(ae(o,s.getResponseHeader("HX-Retarget")))}}const u=Nn(o,i);const r=Pn(s);const a=r.swap;let f=!!r.error;let h=Q.config.ignoreTitle||r.ignoreTitle;let d=r.select;if(r.target){i.target=ue(ae(o,r.target))}var g=e.swapOverride;if(g==null&&r.swapOverride){g=r.swapOverride}if(R(s,/HX-Retarget:/i)){if(s.getResponseHeader("HX-Retarget")==="this"){i.target=o}else{i.target=ue(ae(o,s.getResponseHeader("HX-Retarget")))}}if(R(s,/HX-Reswap:/i)){g=s.getResponseHeader("HX-Reswap")}var p=s.response;var m=ce({shouldSwap:a,serverResponse:p,isError:f,ignoreTitle:h,selectOverride:d,swapOverride:g},i);if(r.event&&!he(l,r.event,m))return;if(!he(l,"htmx:beforeSwap",m))return;l=m.target;p=m.serverResponse;f=m.isError;h=m.ignoreTitle;d=m.selectOverride;g=m.swapOverride;i.target=l;i.failed=f;i.successful=!f;if(m.shouldSwap){if(s.status===286){lt(o)}Ft(o,function(e){p=e.transformResponse(p,s,o)});if(u.type){zt()}var x=gn(o,g);if(!x.hasOwnProperty("ignoreTitle")){x.ignoreTitle=h}l.classList.add(Q.config.swappingClass);let n=null;let r=null;if(c){d=c}if(R(s,/HX-Reselect:/i)){d=s.getResponseHeader("HX-Reselect")}const y=re(o,"hx-select-oob");const b=re(o,"hx-select");let e=function(){try{if(u.type){he(ne().body,"htmx:beforeHistoryUpdate",ce({history:u},i));if(u.type==="push"){$t(u.path);he(ne().body,"htmx:pushedIntoHistory",{path:u.path})}else{Jt(u.path);he(ne().body,"htmx:replacedInHistory",{path:u.path})}}$e(l,p,x,{select:d||b,selectOOB:y,eventInfo:i,anchor:i.pathInfo.anchor,contextElement:o,afterSwapCallback:function(){if(R(s,/HX-Trigger-After-Swap:/i)){let e=o;if(!le(o)){e=ne().body}Je(s,"HX-Trigger-After-Swap",e)}},afterSettleCallback:function(){if(R(s,/HX-Trigger-After-Settle:/i)){let e=o;if(!le(o)){e=ne().body}Je(s,"HX-Trigger-After-Settle",e)}oe(n)}})}catch(e){fe(o,"htmx:swapError",i);oe(r);throw e}};let t=Q.config.globalViewTransitions;if(x.hasOwnProperty("transition")){t=x.transition}if(t&&he(o,"htmx:beforeTransition",i)&&typeof Promise!=="undefined"&&document.startViewTransition){const v=new Promise(function(e,t){n=e;r=t});const w=e;e=function(){document.startViewTransition(function(){w();return v})}}if(x.swapDelay>0){E().setTimeout(e,x.swapDelay)}else{e()}}if(f){fe(o,"htmx:responseError",ce({error:"Response Status Error Code "+s.status+" from "+i.pathInfo.requestPath},i))}}const Mn={};function Xn(){return{init:function(e){return null},getSelectors:function(){return null},onEvent:function(e,t){return true},transformResponse:function(e,t,n){return e},isInlineSwap:function(e){return false},handleSwap:function(e,t,n,r){return false},encodeParameters:function(e,t,n){return null}}}function Fn(e,t){if(t.init){t.init(n)}Mn[e]=ce(Xn(),t)}function Bn(e){delete Mn[e]}function Un(e,n,r){if(n==undefined){n=[]}if(e==undefined){return n}if(r==undefined){r=[]}const t=te(e,"hx-ext");if(t){se(t.split(","),function(e){e=e.replace(/ /g,"");if(e.slice(0,7)=="ignore:"){r.push(e.slice(7));return}if(r.indexOf(e)<0){const t=Mn[e];if(t&&n.indexOf(t)<0){n.push(t)}}})}return Un(ue(c(e)),n,r)}var jn=false;ne().addEventListener("DOMContentLoaded",function(){jn=true});function Vn(e){if(jn||ne().readyState==="complete"){e()}else{ne().addEventListener("DOMContentLoaded",e)}}function _n(){if(Q.config.includeIndicatorStyles!==false){const e=Q.config.inlineStyleNonce?` nonce="${Q.config.inlineStyleNonce}"`:"";ne().head.insertAdjacentHTML("beforeend","<style"+e+">      ."+Q.config.indicatorClass+"{opacity:0}      ."+Q.config.requestClass+" ."+Q.config.indicatorClass+"{opacity:1; transition: opacity 200ms ease-in;}      ."+Q.config.requestClass+"."+Q.config.indicatorClass+"{opacity:1; transition: opacity 200ms ease-in;}      </style>")}}function zn(){const e=ne().querySelector('meta[name="htmx-config"]');if(e){return S(e.content)}else{return null}}function $n(){const e=zn();if(e){Q.config=ce(Q.config,e)}}Vn(function(){$n();_n();let e=ne().body;kt(e);const t=ne().querySelectorAll("[hx-trigger='restored'],[data-hx-trigger='restored']");e.addEventListener("htmx:abort",function(e){const t=e.target;const n=ie(t);if(n&&n.xhr){n.xhr.abort()}});const n=window.onpopstate?window.onpopstate.bind(window):null;window.onpopstate=function(e){if(e.state&&e.state.htmx){Wt();se(t,function(e){he(e,"htmx:restored",{document:ne(),triggerEvent:he})})}else{if(n){n(e)}}};E().setTimeout(function(){he(e,"htmx:load",{});e=null},0)});return Q}();
\ No newline at end of file
diff --git a/core/core.libraries.yml b/core/core.libraries.yml
index cf74707b51e4aa496e4173ffe136f4978113995f..35bf4b0d7a46615e9942762fe9f042e10dc1c4d6 100644
--- a/core/core.libraries.yml
+++ b/core/core.libraries.yml
@@ -614,6 +614,16 @@ drupal.form:
     - core/drupal.debounce
     - core/once
 
+drupal.htmx:
+  version: VERSION
+  js:
+    misc/htmx-behaviors.js: {}
+  dependencies:
+    - core/drupal
+    - core/drupalSettings
+    - core/htmx
+    - core/loadjs
+
 drupal.machine-name:
   version: VERSION
   js:
@@ -782,6 +792,28 @@ drupal.vertical-tabs:
     - core/drupalSettings
     - core/drupal.form
 
+htmx:
+  remote: https://github.com/bigskysoftware/htmx
+  version: "2.0.4"
+  license:
+    name: Zero-Clause BSD
+    url: https://github.com/bigskysoftware/htmx/blob/master/LICENSE
+    gpl-compatible: true
+  js:
+    assets/vendor/htmx/htmx.min.js: { minified: true }
+
+htmx.debug:
+  remote: https://github.com/bigskysoftware/htmx-extensions
+  version: "2.0.1"
+  license:
+    name: Zero-Clause BSD
+    url: https://github.com/bigskysoftware/htmx-extensions/blob/dev/src/debug/LICENSE
+    gpl-compatible: true
+  js:
+    assets/vendor/htmx/debug.js: {}
+  dependencies:
+    - core/htmx
+
 internal.floating-ui:
   remote: https://github.com/floating-ui/floating-ui
   version: "1.6.12"
diff --git a/core/core.services.yml b/core/core.services.yml
index 4372e6512c3e34c73f1db7c5174306690d134bd0..79d276046000d77ea51fcb101036e35352e4f5a7 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1400,6 +1400,14 @@ services:
   html_response.subscriber:
     class: Drupal\Core\EventSubscriber\HtmlResponseSubscriber
     arguments: ['@html_response.attachments_processor']
+  htmx_response.attachments_processor:
+    class: Drupal\Core\Render\Hypermedia\HtmxResponseAttachmentsProcessor
+    arguments: [ '@asset.resolver', '@config.factory', '@asset.css.collection_renderer', '@asset.js.collection_renderer', '@request_stack', '@renderer', '@module_handler', '@language_manager' ]
+  htmx.response_subscriber:
+    class: Drupal\Core\EventSubscriber\HtmxResponseSubscriber
+    arguments: [ '@request_stack', '@htmx_response.attachments_processor' ]
+    tags:
+      - { name: event_subscriber }
   finish_response_subscriber:
     class: Drupal\Core\EventSubscriber\FinishResponseSubscriber
     arguments: ['@language_manager', '@config.factory', '@page_cache_request_policy', '@page_cache_response_policy', '@cache_contexts_manager', '@datetime.time', '%http.response.debug_cacheability_headers%']
diff --git a/core/lib/Drupal/Core/Datetime/Element/Datetime.php b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
index f3b7aba93a450282350077cee59af244b294c92e..e154ab415750f7fab3ebfbb3f1f8e616c32e6eec 100644
--- a/core/lib/Drupal/Core/Datetime/Element/Datetime.php
+++ b/core/lib/Drupal/Core/Datetime/Element/Datetime.php
@@ -52,6 +52,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processDatetime'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
         [static::class, 'processGroup'],
       ],
       '#pre_render' => [
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmxResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmxResponseSubscriber.php
new file mode 100644
index 0000000000000000000000000000000000000000..1a0fa2170317818283c6e83eb6510bec4e34e7dc
--- /dev/null
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmxResponseSubscriber.php
@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Core\EventSubscriber;
+
+use Drupal\Core\Render\AttachmentsResponseProcessorInterface;
+use Drupal\Core\Render\HtmlResponse;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpFoundation\RequestStack;
+use Symfony\Component\HttpKernel\Event\ResponseEvent;
+use Symfony\Component\HttpKernel\KernelEvents;
+
+/**
+ * Adds assets to a header value on responses to HTMX requests.
+ *
+ * Process all attachments before the attachments are rendered in
+ * HtmlResponseSubscriber.
+ *
+ * @see \Drupal\Core\Ajax\HtmxResponseAttachmentsProcessor
+ */
+final class HtmxResponseSubscriber implements EventSubscriberInterface {
+
+  /**
+   * Constructs a HtmxResponseSubscriber object.
+   */
+  public function __construct(
+    private readonly RequestStack $requestStack,
+    private readonly AttachmentsResponseProcessorInterface $attachmentsProcessor,
+  ) {}
+
+  /**
+   * Add assemble and attachments add HTMX attributes.
+   *
+   * @see \Drupal\Core\EventSubscriber\HtmlResponseSubscriber::onRespond
+   */
+  public function onRespond(ResponseEvent $event): void {
+    $response = $event->getResponse();
+    $requestHeaders = $this->requestStack->getCurrentRequest()->headers;
+    if (!($response instanceof HtmlResponse && $requestHeaders->has('HX-Request'))) {
+      // Only operate on HTML responses from an HTMX request.
+      return;
+    }
+    $processedResponse = $this->attachmentsProcessor->processAttachments($response);
+    if (!($processedResponse instanceof HtmlResponse)) {
+      throw new \TypeError("ResponseEvent::setResponse() requires an HtmlResponse object");
+    }
+    $event->setResponse($processedResponse);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    return [
+      // Our method needs to run before the HtmlResponseSubscriber(weight 0).
+      KernelEvents::RESPONSE => ['onRespond', 100],
+    ];
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Form/FormBase.php b/core/lib/Drupal/Core/Form/FormBase.php
index d88810943acd0dc6763195c2dd4357192b41b444..4892e20cdf5e5307aa5aa1efbba199216aa32159 100644
--- a/core/lib/Drupal/Core/Form/FormBase.php
+++ b/core/lib/Drupal/Core/Form/FormBase.php
@@ -194,6 +194,28 @@ protected function currentUser() {
     return \Drupal::currentUser();
   }
 
+  /**
+   * True if the HX-Request header was present on the request.
+   *
+   * @return bool
+   *   Is this an HTMX request?
+   */
+  public function isHtmxRequest(): bool {
+    $request = $this->getRequest();
+    return $request->headers->has('HX-Request');
+  }
+
+  /**
+   * Returns the HTMX trigger value stored from the request.
+   *
+   * @return string
+   *   The trigger name or empty string if the header is not present.
+   */
+  public function getHtmxTrigger(): string {
+    $request = $this->getRequest();
+    return $request->headers->get('HX-Trigger', '');
+  }
+
   /**
    * Returns a redirect response object for the specified route.
    *
diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index ee3e4893feca035c00a95603554569bb00c3d052..650ea21e83f888b3d3ef2d20a46a90eab370d718 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -17,6 +17,7 @@
 use Drupal\Core\Render\ElementInfoManagerInterface;
 use Drupal\Core\Security\TrustedCallbackInterface;
 use Drupal\Core\Theme\ThemeManagerInterface;
+use Symfony\Component\HttpFoundation\Request;
 use Symfony\Contracts\EventDispatcher\EventDispatcherInterface;
 use Symfony\Component\HttpFoundation\FileBag;
 use Symfony\Component\HttpFoundation\InputBag;
@@ -302,8 +303,10 @@ public function buildForm($form_arg, FormStateInterface &$form_state) {
       }
     }
 
-    // If this form is an AJAX request, disable all form redirects.
-    if ($ajax_form_request = $request->query->has(static::AJAX_FORM_REQUEST)) {
+    // If this form is a jQuery AJAX request, or an HTMX request disable all
+    // form redirects.
+    $ajax_form_request = $request->query->has(static::AJAX_FORM_REQUEST);
+    if ($ajax_form_request || $this->isHtmxRequest($request)) {
       $form_state->disableRedirect();
     }
 
@@ -602,6 +605,19 @@ public function processForm($form_id, &$form, FormStateInterface &$form_state) {
         return;
       }
 
+      // If a form from an HTMX request is still processing at this point it
+      // was not submitted.  The form_build_id value needs to be restored if
+      // the form rebuilds.
+      // @see \Drupal\Core\Form\EventSubscriber\FormAjaxSubscriber::onException
+      // @see Drupal.AjaxCommands.update_build_id
+      if ($this->isHtmxRequest()) {
+        // Restore the build id that was sent with the request. It will be used
+        // after the rebuild to cache the rebuilt form.
+        $form_state->addRebuildInfo('copy', ['#build_id' => TRUE]);
+        $input = $form_state->getUserInput();
+        $form['#build_id'] = $input['form_build_id'];
+      }
+
       // If $form_state->isRebuilding() has been set and input has been
       // processed without validation errors, we are in a multi-step workflow
       // that is not yet complete. A new $form needs to be constructed based on
@@ -1299,7 +1315,7 @@ protected function handleInputElement($form_id, &$element, FormStateInterface &$
     // \Drupal\Core\Form\FormState::cleanValues(). Enforce the same input
     // processing restrictions as above.
     if ($process_input) {
-      // Detect if the element triggered the submission via Ajax.
+      // Detect if the element triggered the submission via Ajax or HTMX.
       if ($this->elementTriggeredScriptedSubmission($element, $form_state)) {
         $form_state->setTriggeringElement($element);
       }
@@ -1342,6 +1358,12 @@ protected function handleInputElement($form_id, &$element, FormStateInterface &$
    */
   protected function elementTriggeredScriptedSubmission($element, FormStateInterface &$form_state) {
     $input = $form_state->getUserInput();
+    if ($this->isHtmxRequest()) {
+      if (isset($element['#attributes']['data-drupal-selector']) && $element['#attributes']['data-drupal-selector'] === $this->getHtmxTrigger()) {
+        // @see htmxDrupalData() in core/misc/htmx-behaviors.js.
+        return TRUE;
+      }
+    }
     if (!empty($input['_triggering_element_name']) && $element['#name'] == $input['_triggering_element_name']) {
       if (empty($input['_triggering_element_value']) || $input['_triggering_element_value'] == $element['#value']) {
         return TRUE;
@@ -1419,6 +1441,38 @@ protected function currentUser() {
     return $this->currentUser;
   }
 
+  /**
+   * True if the HX-Request header was present on the request.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request|null $request
+   *   A Request to use.  If omitted, the current request on the stack is used.
+   *
+   * @return bool
+   *   Is this an HTMX request?
+   */
+  public function isHtmxRequest(?Request $request = NULL): bool {
+    if (!($request instanceof Request)) {
+      $request = $this->requestStack->getCurrentRequest();
+    }
+    return $request->headers->has('HX-Request');
+  }
+
+  /**
+   * Returns the HTMX trigger value stored from the request.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request|null $request
+   *   A Request to use.  If omitted, the current request on the stack is used.
+   *
+   * @return string
+   *   The trigger name or empty string if the header is not present.
+   */
+  public function getHtmxTrigger(?Request $request = NULL): string {
+    if (!($request instanceof Request)) {
+      $request = $this->requestStack->getCurrentRequest();
+    }
+    return $request->headers->get('HX-Trigger', '');
+  }
+
   /**
    * {@inheritdoc}
    */
diff --git a/core/lib/Drupal/Core/Http/HtmxHeaderInterface.php b/core/lib/Drupal/Core/Http/HtmxHeaderInterface.php
new file mode 100644
index 0000000000000000000000000000000000000000..f1cd52b352899efe97ce184e1fddced32c6f1965
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/HtmxHeaderInterface.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace Drupal\Core\Http;
+
+/**
+ * An interface for classes that manage HTMX Headers.
+ *
+ * @extends \IteratorAggregate<string, list<string|null>>
+ */
+interface HtmxHeaderInterface extends \IteratorAggregate, \Countable, \Stringable {
+
+  /**
+   * Checks if the storage has a header with the given name.
+   *
+   * @param string $name
+   *   The name of the header to check for.
+   *
+   * @return bool
+   *   Returns TRUE if the header exists, or FALSE otherwise.
+   */
+  public function hasHeader(string $name): bool;
+
+  /**
+   * Returns all storage elements as a Drupal 'http_header' array.
+   *
+   * @return mixed[]
+   *   An associative array of headers.
+   */
+  public function toArray(): array;
+
+  /**
+   * Merges an HtmxHeaderInterface object into the current storage.
+   *
+   * @param HtmlAttributeInterface $headers
+   *   The Attribute object to merge.
+   *
+   * @return HtmxHeaderInterface
+   *   A combined header collection.
+   */
+  public function merge(HtmxHeaderInterface $headers): HtmxHeaderInterface;
+
+}
diff --git a/core/lib/Drupal/Core/Http/HtmxLocationResponseData.php b/core/lib/Drupal/Core/Http/HtmxLocationResponseData.php
new file mode 100644
index 0000000000000000000000000000000000000000..4fee738040ab1132cae1823a2e89d793b3c722fe
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/HtmxLocationResponseData.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace Drupal\Core\Http;
+
+use Drupal\Core\Url;
+
+/**
+ * Optional data object for HX-Location.
+ */
+class HtmxLocationResponseData implements \Stringable {
+
+  /**
+   * Data for HX-Location headers.
+   *
+   * @param \Drupal\Core\Url $path
+   *   The path for the GET request.
+   * @param string $source
+   *   The source element of the request.
+   * @param string $event
+   *   An event that “triggered” the request.
+   * @param array<string, string> $headers
+   *   Headers to submit with the request.
+   * @param string $handler
+   *   A callback that will handle the response HTML.
+   * @param string $target
+   *   The target for the swap.
+   * @param string $swap
+   *   The swap strategy.
+   * @param string $select
+   *   A selector for the content to swap into the target.
+   * @param array<string, string> $values
+   *   A set of values to submit with the request.
+   *
+   * @see https://htmx.org/headers/hx-location/
+   */
+  public function __construct(
+    public readonly Url $path,
+    public readonly string $source = '',
+    public readonly string $event = '',
+    public readonly array $headers = [],
+    public readonly string $handler = '',
+    public readonly string $target = '',
+    public readonly string $swap = '',
+    public readonly string $select = '',
+    public readonly array $values = [],
+  ) {}
+
+  /**
+   * Returns non-empty data, JSON encoded.
+   *
+   * @return string
+   *   The encoded data.
+   */
+  public function __toString(): string {
+    $data = [
+      'path' => $this->path->toString(),
+      'source' => $this->source,
+      'event' => $this->event,
+      'headers' => $this->headers,
+      'handler' => $this->handler,
+      'target' => $this->target,
+      'swap' => $this->swap,
+      'select' => $this->select,
+      'values' => $this->values,
+    ];
+    $data = array_filter($data, static fn ($item) => $item !== '' && $item !== []);
+    return json_encode($data);
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Http/HtmxResponseHeaders.php b/core/lib/Drupal/Core/Http/HtmxResponseHeaders.php
new file mode 100644
index 0000000000000000000000000000000000000000..20439a79631e7e8472043ab4550823b04d68b100
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/HtmxResponseHeaders.php
@@ -0,0 +1,279 @@
+<?php
+
+namespace Drupal\Core\Http;
+
+use Drupal\Core\Url;
+use Symfony\Component\HttpFoundation\HeaderBag;
+
+/**
+ * Builds HTMX response headers.
+ *
+ * Principally used in the composite Htmx value object.
+ *
+ * @see \Drupal\Core\Render\Hypermedia\Htmx
+ * @see https://htmx.org/reference/#response_headers
+ */
+class HtmxResponseHeaders implements HtmxHeaderInterface {
+
+  /**
+   * Initialize empty storage.
+   *
+   * Allows for passing a populated HeaderBag to support merging.
+   */
+  public function __construct(
+    private HeaderBag $headers = new HeaderBag(),
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIterator(): \Traversable {
+    return $this->headers->getIterator();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count(): int {
+    return $this->headers->count();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __toString(): string {
+    return (string) $this->headers;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasHeader($name): bool {
+    return $this->headers->has($name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function toArray(): array {
+    $drupalHeaders = [];
+    foreach ($this->headers as $name => $value) {
+      // Set replace to true.
+      $drupalHeaders[] = [$name, $value, TRUE];
+    }
+    return $drupalHeaders;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function merge(HtmxHeaderInterface $headers): HtmxHeaderInterface {
+    foreach ($headers as $name => $value) {
+      $this->headers->set($name, $value);
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Location header.
+   *
+   * @param \Drupal\Core\Url|\Drupal\htmx\Http\HtmxLocationResponseData $data
+   *   Use Url if only a path is needed.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-location/
+   */
+  public function location(Url|HtmxLocationResponseData $data): HtmxResponseHeaders {
+    if ($data instanceof HtmxLocationResponseData) {
+      $this->headers->set('HX-Location', (string) $data);
+    }
+    else {
+      $this->headers->set('HX-Location', $data->toString());
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Push-Url header.
+   *
+   * @param \Drupal\Core\Url|false $data
+   *   URL to push to the location bar or false to prevent a history update.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-push-url/
+   */
+  public function pushUrl(Url|false $data): HtmxResponseHeaders {
+    if ($data instanceof Url) {
+      $this->headers->set('HX-Push-Url', $data->toString());
+    }
+    else {
+      $this->headers->set('HX-Push-Url', 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Replace-Url header.
+   *
+   * @param \Drupal\Core\Url|false $data
+   *   URL for history replacement, false  prevents updates to the current URL.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-replace-url/
+   */
+  public function replaceUrl(Url|false $data): HtmxResponseHeaders {
+    if ($data instanceof Url) {
+      $this->headers->set('HX-Replace-Url', $data->toString());
+    }
+    else {
+      $this->headers->set('HX-Replace-Url', 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Redirect header.
+   *
+   * @param \Drupal\Core\Url $url
+   *   Destination for a client side redirection.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   */
+  public function redirect(Url $url): HtmxResponseHeaders {
+    $this->headers->set('HX-Redirect', $url->toString());
+    return $this;
+  }
+
+  /**
+   * Set HX-Refresh header.
+   *
+   * @param bool $refresh
+   *   If set to “true” the client-side will do a full refresh of the page.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   */
+  public function refresh(bool $refresh): HtmxResponseHeaders {
+    $this->headers->set('HX-Refresh', $refresh ? 'true' : 'false');
+    return $this;
+  }
+
+  /**
+   * Set HX-Reswap header.
+   *
+   * @param string $strategy
+   *   Specify how the response will be swapped (see hx-swap).
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   */
+  public function reswap(string $strategy): HtmxResponseHeaders {
+    $this->headers->set('HX-Reswap', $strategy);
+    return $this;
+  }
+
+  /**
+   * Set HX-Retarget header.
+   *
+   * @param string $strategy
+   *   CSS selector that replaces the target to a different element on the page.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   */
+  public function retarget(string $strategy): HtmxResponseHeaders {
+    $this->headers->set('HX-Retarget', $strategy);
+    return $this;
+  }
+
+  /**
+   * Set HX-Reselect header.
+   *
+   * @param string $strategy
+   *   CSS selector that changes the selection taken from the response.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   */
+  public function reselect(string $strategy): HtmxResponseHeaders {
+    $this->headers->set('HX-Reselect', $strategy);
+    return $this;
+  }
+
+  /**
+   * Set HX-Trigger header.
+   *
+   * See the documentation for the structure of the array.
+   *
+   * @param string|array $data
+   *   An event name or an array which will be JSON encoded.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-trigger/
+   */
+  public function trigger(string|array $data): HtmxResponseHeaders {
+    if (is_array($data)) {
+      $this->headers->set('HX-Trigger', json_encode($data));
+    }
+    else {
+      $this->headers->set('HX-Trigger', $data);
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Trigger-After-Settle header.
+   *
+   * See the documentation for the structure of the array.
+   *
+   * @param string|array $data
+   *   An event name or an array which will be JSON encoded.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-trigger/
+   */
+  public function triggerAfterSettle(string|array $data): HtmxResponseHeaders {
+    if (is_array($data)) {
+      $this->headers->set('HX-Trigger-After-Settle', json_encode($data));
+    }
+    else {
+      $this->headers->set('HX-Trigger-After-Settle', $data);
+    }
+    return $this;
+  }
+
+  /**
+   * Set HX-Trigger-After-Swap header.
+   *
+   * See the documentation for the structure of the array.
+   *
+   * @param string|array $data
+   *   An event name or an array which will be JSON encoded.
+   *
+   * @return \Drupal\htmx\Http\HtmxResponseHeaders
+   *   Self for chaining.
+   *
+   * @see https://htmx.org/headers/hx-trigger/
+   */
+  public function triggerAfterSwap(string|array $data): HtmxResponseHeaders {
+    if (is_array($data)) {
+      $this->headers->set('HX-Trigger-After-Swap', json_encode($data));
+    }
+    else {
+      $this->headers->set('HX-Trigger-After-Swap', $data);
+    }
+    return $this;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Http/HttpMethod.php b/core/lib/Drupal/Core/Http/HttpMethod.php
new file mode 100644
index 0000000000000000000000000000000000000000..52637d601736f989da6519c3ef2c511dab613166
--- /dev/null
+++ b/core/lib/Drupal/Core/Http/HttpMethod.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace Drupal\Core\Http;
+
+/**
+ * Enumerates the valid HTTP methods or verbs.
+ */
+enum HttpMethod {
+
+  case Get;
+  case Post;
+  case Put;
+  case Patch;
+  case Delete;
+
+}
diff --git a/core/lib/Drupal/Core/Render/Element/Button.php b/core/lib/Drupal/Core/Render/Element/Button.php
index a8f12e93963690cbcf909789678489de57420cc7..7712e394f067772bfba2d2807c6c4b72d55ae1ff 100644
--- a/core/lib/Drupal/Core/Render/Element/Button.php
+++ b/core/lib/Drupal/Core/Render/Element/Button.php
@@ -53,6 +53,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processButton'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderButton'],
diff --git a/core/lib/Drupal/Core/Render/Element/Checkbox.php b/core/lib/Drupal/Core/Render/Element/Checkbox.php
index 65be5d22bf106195fe50894a7823f684f8cefe1b..2380fc5328b507024e5e4bbbd585742033c62cb6 100644
--- a/core/lib/Drupal/Core/Render/Element/Checkbox.php
+++ b/core/lib/Drupal/Core/Render/Element/Checkbox.php
@@ -35,6 +35,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processCheckbox'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
         [static::class, 'processGroup'],
       ],
       '#pre_render' => [
diff --git a/core/lib/Drupal/Core/Render/Element/Color.php b/core/lib/Drupal/Core/Render/Element/Color.php
index 254300d976f9b11c0871b3f607e76078819b7013..0c031a813e33fc78376548fa62a97289d915ebed 100644
--- a/core/lib/Drupal/Core/Render/Element/Color.php
+++ b/core/lib/Drupal/Core/Render/Element/Color.php
@@ -33,6 +33,7 @@ public function getInfo() {
       '#input' => TRUE,
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#element_validate' => [
         [static::class, 'validateColor'],
diff --git a/core/lib/Drupal/Core/Render/Element/Container.php b/core/lib/Drupal/Core/Render/Element/Container.php
index d5a2092718e742454abf7d7ab416e2cda2cfd238..83b400525d29db059f91457b284cdde32aee6c6c 100644
--- a/core/lib/Drupal/Core/Render/Element/Container.php
+++ b/core/lib/Drupal/Core/Render/Element/Container.php
@@ -58,6 +58,7 @@ public function getInfo() {
       '#pre_render' => [
         [static::class, 'preRenderGroup'],
         [static::class, 'preRenderContainer'],
+        [static::class, 'processHtmxElement'],
       ],
       '#theme_wrappers' => ['container'],
     ];
diff --git a/core/lib/Drupal/Core/Render/Element/Date.php b/core/lib/Drupal/Core/Render/Element/Date.php
index 8304167ae70782ea9791bcf390354a38100a6589..cd97a6031481ec6958693d8f489c2be9465e8511 100644
--- a/core/lib/Drupal/Core/Render/Element/Date.php
+++ b/core/lib/Drupal/Core/Render/Element/Date.php
@@ -45,6 +45,7 @@ public function getInfo() {
       '#theme' => 'input__date',
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [[static::class, 'preRenderDate']],
       '#theme_wrappers' => ['form_element'],
diff --git a/core/lib/Drupal/Core/Render/Element/Details.php b/core/lib/Drupal/Core/Render/Element/Details.php
index 28e7396887d8b3c6c673602a1b97eba364b09af8..b4b24f74631e90c461b3119c19ee6ef8ef178faf 100644
--- a/core/lib/Drupal/Core/Render/Element/Details.php
+++ b/core/lib/Drupal/Core/Render/Element/Details.php
@@ -49,6 +49,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processGroup'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderDetails'],
diff --git a/core/lib/Drupal/Core/Render/Element/Dropbutton.php b/core/lib/Drupal/Core/Render/Element/Dropbutton.php
index 20bb375ea879f32a4c1097aced634fbbf547af97..09c43ed64da3dc127aeeed33e66b1e09f9845fc3 100644
--- a/core/lib/Drupal/Core/Render/Element/Dropbutton.php
+++ b/core/lib/Drupal/Core/Render/Element/Dropbutton.php
@@ -52,6 +52,7 @@ public function getInfo() {
     return [
       '#pre_render' => [
         [static::class, 'preRenderDropbutton'],
+        [static::class, 'processHtmxElement'],
       ],
       '#theme' => 'links__dropbutton',
     ];
diff --git a/core/lib/Drupal/Core/Render/Element/Email.php b/core/lib/Drupal/Core/Render/Element/Email.php
index 82e688ce38e2cc86671c44c9dc0fef63955bb570..71b22e1079a921c3e4a5ba1041960e0f31903367 100644
--- a/core/lib/Drupal/Core/Render/Element/Email.php
+++ b/core/lib/Drupal/Core/Render/Element/Email.php
@@ -53,6 +53,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processAutocomplete'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
         [static::class, 'processPattern'],
       ],
       '#element_validate' => [
diff --git a/core/lib/Drupal/Core/Render/Element/Fieldset.php b/core/lib/Drupal/Core/Render/Element/Fieldset.php
index af0396789b39bfee7bb7f808bddfd67c620831cf..6a65c8b64000c472e01cd3cd1c7a743e6abca0a1 100644
--- a/core/lib/Drupal/Core/Render/Element/Fieldset.php
+++ b/core/lib/Drupal/Core/Render/Element/Fieldset.php
@@ -34,6 +34,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processGroup'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderGroup'],
diff --git a/core/lib/Drupal/Core/Render/Element/Hidden.php b/core/lib/Drupal/Core/Render/Element/Hidden.php
index db3b23a08cced0fcf51b8bfc7732485522dfced9..98c524b14be6c335fb966e7f9f290523dcb7cdf4 100644
--- a/core/lib/Drupal/Core/Render/Element/Hidden.php
+++ b/core/lib/Drupal/Core/Render/Element/Hidden.php
@@ -34,6 +34,7 @@ public function getInfo() {
       '#input' => TRUE,
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderHidden'],
diff --git a/core/lib/Drupal/Core/Render/Element/HtmlTag.php b/core/lib/Drupal/Core/Render/Element/HtmlTag.php
index 3b4dbd25d462f1547cbc3137d1012383fff2cb87..d59e4189c417677d32ef878a9e7b3ee1383bdad7 100644
--- a/core/lib/Drupal/Core/Render/Element/HtmlTag.php
+++ b/core/lib/Drupal/Core/Render/Element/HtmlTag.php
@@ -56,6 +56,7 @@ public function getInfo() {
     return [
       '#pre_render' => [
         [static::class, 'preRenderHtmlTag'],
+        [static::class, 'processHtmxElement'],
       ],
       '#attributes' => [],
       '#value' => NULL,
diff --git a/core/lib/Drupal/Core/Render/Element/Label.php b/core/lib/Drupal/Core/Render/Element/Label.php
index b2dbc9841a73e80c58e4dbc6317afc0f2824175f..cefbe049adfec91d1ed5ae42db65c7a63e31a9d6 100644
--- a/core/lib/Drupal/Core/Render/Element/Label.php
+++ b/core/lib/Drupal/Core/Render/Element/Label.php
@@ -20,6 +20,9 @@ class Label extends RenderElementBase {
   public function getInfo() {
     return [
       '#theme' => 'form_element_label',
+      '#pre_render' => [
+        [self::class, 'processHtmxElement'],
+      ],
     ];
   }
 
diff --git a/core/lib/Drupal/Core/Render/Element/Link.php b/core/lib/Drupal/Core/Render/Element/Link.php
index 2a00e0526b6872640f18057a2e67585e00298df5..73d4e6f149a9965838c9c9eb5cbc3ea688c6dfd2 100644
--- a/core/lib/Drupal/Core/Render/Element/Link.php
+++ b/core/lib/Drupal/Core/Render/Element/Link.php
@@ -37,6 +37,7 @@ public function getInfo() {
     return [
       '#pre_render' => [
         [static::class, 'preRenderLink'],
+        [static::class, 'processHtmxElement'],
       ],
     ];
   }
diff --git a/core/lib/Drupal/Core/Render/Element/MachineName.php b/core/lib/Drupal/Core/Render/Element/MachineName.php
index ec03e46616e8714bec82669844e51f9c8ec20ee5..b6935fd0f8f2ca67238f31bebba71d8ff864d476 100644
--- a/core/lib/Drupal/Core/Render/Element/MachineName.php
+++ b/core/lib/Drupal/Core/Render/Element/MachineName.php
@@ -88,6 +88,7 @@ public function getInfo() {
         [static::class, 'processMachineName'],
         [static::class, 'processAutocomplete'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#element_validate' => [
         [static::class, 'validateMachineName'],
diff --git a/core/lib/Drupal/Core/Render/Element/Number.php b/core/lib/Drupal/Core/Render/Element/Number.php
index 7096b2925beb6dbece49b9b613aa0e10b15e56de..c15da7339434ebfd19f128edcd1a5aa42a3ed3b9 100644
--- a/core/lib/Drupal/Core/Render/Element/Number.php
+++ b/core/lib/Drupal/Core/Render/Element/Number.php
@@ -41,6 +41,7 @@ public function getInfo() {
       '#step' => 1,
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#element_validate' => [
         [static::class, 'validateNumber'],
diff --git a/core/lib/Drupal/Core/Render/Element/PageTitle.php b/core/lib/Drupal/Core/Render/Element/PageTitle.php
index c56141de3480c7e850cbc8cc45f466f39754830a..de8bf1ea1fdd9898076ffcaccc96368047b1dcbc 100644
--- a/core/lib/Drupal/Core/Render/Element/PageTitle.php
+++ b/core/lib/Drupal/Core/Render/Element/PageTitle.php
@@ -21,6 +21,9 @@ public function getInfo() {
       // The page title: either a string for plain titles or a render array for
       // formatted titles.
       '#title' => NULL,
+      '#pre_render' => [
+        [self::class, 'processHtmxElement'],
+      ],
     ];
   }
 
diff --git a/core/lib/Drupal/Core/Render/Element/Pager.php b/core/lib/Drupal/Core/Render/Element/Pager.php
index a31c7f2f37190ff6768562c59aad7904dcd46d79..bf8cc4fff4ad7b58ae7b6039e972534eaad7efd9 100644
--- a/core/lib/Drupal/Core/Render/Element/Pager.php
+++ b/core/lib/Drupal/Core/Render/Element/Pager.php
@@ -41,6 +41,7 @@ public function getInfo() {
     return [
       '#pre_render' => [
         static::class . '::preRenderPager',
+        [self::class, 'processHtmxElement'],
       ],
       '#theme' => 'pager',
       // The pager ID, to distinguish between multiple pagers on the same page.
diff --git a/core/lib/Drupal/Core/Render/Element/Password.php b/core/lib/Drupal/Core/Render/Element/Password.php
index 0c2e99d054b73758265afff62bdc3b778e741ca0..c8abaa99cd497318ff895c891f7354775c80fb8e 100644
--- a/core/lib/Drupal/Core/Render/Element/Password.php
+++ b/core/lib/Drupal/Core/Render/Element/Password.php
@@ -39,6 +39,7 @@ public function getInfo() {
       '#maxlength' => 128,
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
         [static::class, 'processPattern'],
       ],
       '#pre_render' => [
diff --git a/core/lib/Drupal/Core/Render/Element/Radio.php b/core/lib/Drupal/Core/Render/Element/Radio.php
index e7c5771ec4c537b868a468bc075b082bda0df030..33e3e5c8c4bf43fc6f33690ff3ecb0d7f48b25bf 100644
--- a/core/lib/Drupal/Core/Render/Element/Radio.php
+++ b/core/lib/Drupal/Core/Render/Element/Radio.php
@@ -26,6 +26,7 @@ public function getInfo() {
       '#default_value' => NULL,
       '#process' => [
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderRadio'],
diff --git a/core/lib/Drupal/Core/Render/Element/RenderElementBase.php b/core/lib/Drupal/Core/Render/Element/RenderElementBase.php
index 451df8a0e3695cfc86dff67bfbdb64f1439818fb..cae21eb90326a5c05bd8790f92aa9c48444d707c 100644
--- a/core/lib/Drupal/Core/Render/Element/RenderElementBase.php
+++ b/core/lib/Drupal/Core/Render/Element/RenderElementBase.php
@@ -2,11 +2,14 @@
 
 namespace Drupal\Core\Render\Element;
 
+use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Form\FormBuilderInterface;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Plugin\PluginBase;
 use Drupal\Core\Render\BubbleableMetadata;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Render\Hypermedia\HtmxInterface;
+use Drupal\Core\Template\AttributeHelper;
 use Drupal\Core\Url;
 
 /**
@@ -49,8 +52,8 @@
  *   See the "Attaching libraries in render arrays" section of the
  *   @link theme_render Render API topic @endlink for an overview, and
  *   \Drupal\Core\Render\AttachmentsResponseProcessorInterface::processAttachments
- *   for a list of what this can contain. Besides this list, it may also contain
- *   a 'placeholders' element; see the Placeholders section of the
+ *   for a list of what this can contain. Besides this list, it may also
+ *   contain a 'placeholders' element; see the Placeholders section of the
  *   @link theme_render Render API topic @endlink for an overview.
  * - #attributes: (array) HTML attributes for the element. The first-level
  *   keys are the attribute names, such as 'class', and the attributes are
@@ -434,6 +437,51 @@ public static function preRenderAjaxForm($element) {
     return $element;
   }
 
+  /**
+   * @param mixed[] $element
+   *   The render array for the element.
+   *
+   * @return mixed[]
+   *   The modified array with HTMX library attachments, if appropriate.
+   */
+  public static function processHtmxElement(array $element): array {
+    $processed = $element['#htmx_processed'] ?? FALSE;
+    // Skip already processed elements.
+    if ($processed) {
+      return $element;
+    }
+    // Initialize #htmx_processed, so we do not process this element again.
+    $element['#htmx_processed'] = FALSE;
+
+    // Nothing to do if there are no HTMX settings.
+    if (empty($element['#htmx']) || !($element['#htmx'] instanceof HtmxInterface)) {
+      return $element;
+    }
+    $htmx = $element['#htmx'];
+
+    // Process operations;
+    if ($htmx->hasOperations()) {
+      $htmx->processOperations();
+    }
+
+    // Attach HTMX and integration javascript.
+    $element['#attached']['library'][] = 'core/drupal.htmx';
+    // Consolidate headers.
+    if ($htmx->headers->count() !== 0) {
+      $element['#attached']['http_header'] = $element['#attached']['http_header'] ?? [];
+      $element['#attached']['http_header'] = NestedArray::mergeDeep($element['#attached']['http_header'], $htmx->headers->toArray());
+    }
+    if ($htmx->attributes->count() !== 0) {
+      // Consolidate attributes.
+      $element['#attributes'] = $element['#attributes'] ?? [];
+      $element['#attributes'] = AttributeHelper::mergeCollections($element['#attributes'], $htmx->attributes);
+    }
+
+    // Indicate that HTMX processing was successful.
+    $element['#htmx_processed'] = TRUE;
+    return $element;
+  }
+
   /**
    * Arranges elements into groups.
    *
diff --git a/core/lib/Drupal/Core/Render/Element/Search.php b/core/lib/Drupal/Core/Render/Element/Search.php
index 3c022c55e33b1786108c59500428b4533f012308..6d0f36a2520ae1e57cacdc21f932cb5b4ecf3bad 100644
--- a/core/lib/Drupal/Core/Render/Element/Search.php
+++ b/core/lib/Drupal/Core/Render/Element/Search.php
@@ -33,6 +33,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processAutocomplete'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderSearch'],
diff --git a/core/lib/Drupal/Core/Render/Element/Select.php b/core/lib/Drupal/Core/Render/Element/Select.php
index 094b963212bd784c8f0ec3fd96fd3c7397e87df8..5f68df3184904a0b920cb01403693570017784b9 100644
--- a/core/lib/Drupal/Core/Render/Element/Select.php
+++ b/core/lib/Drupal/Core/Render/Element/Select.php
@@ -98,6 +98,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processSelect'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderSelect'],
diff --git a/core/lib/Drupal/Core/Render/Element/StatusMessages.php b/core/lib/Drupal/Core/Render/Element/StatusMessages.php
index 4eecd9f42f1a793d6317fefdfb7259315115cc89..ff03b475b0a322e04a670f3aaa88f8cdf1503dbf 100644
--- a/core/lib/Drupal/Core/Render/Element/StatusMessages.php
+++ b/core/lib/Drupal/Core/Render/Element/StatusMessages.php
@@ -32,6 +32,7 @@ public function getInfo() {
       '#display' => NULL,
       '#pre_render' => [
         static::class . '::generatePlaceholder',
+        [self::class, 'processHtmxElement'],
       ],
       '#include_fallback' => FALSE,
     ];
diff --git a/core/lib/Drupal/Core/Render/Element/Tel.php b/core/lib/Drupal/Core/Render/Element/Tel.php
index 9d5951e7d4e66cfc83b2877f5186e96af427e6a6..9628607e4e8767e69f99d6c2b5e778b9414619dc 100644
--- a/core/lib/Drupal/Core/Render/Element/Tel.php
+++ b/core/lib/Drupal/Core/Render/Element/Tel.php
@@ -42,6 +42,7 @@ public function getInfo() {
         [static::class, 'processAutocomplete'],
         [static::class, 'processAjaxForm'],
         [static::class, 'processPattern'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderTel'],
diff --git a/core/lib/Drupal/Core/Render/Element/Textarea.php b/core/lib/Drupal/Core/Render/Element/Textarea.php
index c3fc6021924436105a89b1f3b80c66901a2eeedb..7fcd4cf81cf96f7a7467b9121bf7efaffeed9182 100644
--- a/core/lib/Drupal/Core/Render/Element/Textarea.php
+++ b/core/lib/Drupal/Core/Render/Element/Textarea.php
@@ -41,6 +41,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processAjaxForm'],
         [static::class, 'processGroup'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderGroup'],
diff --git a/core/lib/Drupal/Core/Render/Element/Textfield.php b/core/lib/Drupal/Core/Render/Element/Textfield.php
index de144ab4348df6dfc0f502a6ba3a652a89004c87..3a04f82145b0c8b8f54a9aa7f0b9d932a237ee20 100644
--- a/core/lib/Drupal/Core/Render/Element/Textfield.php
+++ b/core/lib/Drupal/Core/Render/Element/Textfield.php
@@ -52,6 +52,7 @@ public function getInfo() {
         [static::class, 'processAjaxForm'],
         [static::class, 'processPattern'],
         [static::class, 'processGroup'],
+        [static::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderTextfield'],
diff --git a/core/lib/Drupal/Core/Render/Element/Url.php b/core/lib/Drupal/Core/Render/Element/Url.php
index 7c5a9af2fbb458978c9e06e98a1ef0c70e925ab2..f3f20d2f3e9f80c14b06402ebf6c0614d83fb2b6 100644
--- a/core/lib/Drupal/Core/Render/Element/Url.php
+++ b/core/lib/Drupal/Core/Render/Element/Url.php
@@ -44,6 +44,7 @@ public function getInfo() {
         [static::class, 'processAutocomplete'],
         [static::class, 'processAjaxForm'],
         [static::class, 'processPattern'],
+        [static::class, 'processHtmxElement'],
       ],
       '#element_validate' => [
         [static::class, 'validateUrl'],
diff --git a/core/lib/Drupal/Core/Render/Element/VerticalTabs.php b/core/lib/Drupal/Core/Render/Element/VerticalTabs.php
index bf55119913b0aaad257355f662e45fe24fb9a6a7..b580aee0bad3af3c2e1af331a3029833d01b125e 100644
--- a/core/lib/Drupal/Core/Render/Element/VerticalTabs.php
+++ b/core/lib/Drupal/Core/Render/Element/VerticalTabs.php
@@ -57,6 +57,7 @@ public function getInfo() {
       '#default_tab' => '',
       '#process' => [
         [static::class, 'processVerticalTabs'],
+        [self::class, 'processHtmxElement'],
       ],
       '#pre_render' => [
         [static::class, 'preRenderVerticalTabs'],
diff --git a/core/lib/Drupal/Core/Render/Element/Weight.php b/core/lib/Drupal/Core/Render/Element/Weight.php
index 89df69b1879f9958c176068412e26024b36ea807..c031ff247c38152a2ef56c95acb2dfa929dc92c7 100644
--- a/core/lib/Drupal/Core/Render/Element/Weight.php
+++ b/core/lib/Drupal/Core/Render/Element/Weight.php
@@ -39,6 +39,7 @@ public function getInfo() {
       '#process' => [
         [static::class, 'processWeight'],
         [static::class, 'processAjaxForm'],
+        [static::class, 'processHtmxElement'],
       ],
     ];
   }
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Htmx.php b/core/lib/Drupal/Core/Render/Hypermedia/Htmx.php
new file mode 100644
index 0000000000000000000000000000000000000000..e8bb402d7c665d9a99b08e40f730fdad39bc36dd
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Htmx.php
@@ -0,0 +1,178 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia;
+
+use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Http\HtmxHeaderInterface;
+use Drupal\Core\Http\HtmxResponseHeaders;
+use Drupal\Core\Render\Hypermedia\Operations\HtmxOperationInterface;
+use Drupal\Core\Render\Hypermedia\Operations\HtmxRequestOperationInterface;
+use Drupal\Core\Template\AttributeHelper;
+use Drupal\Core\Template\HtmlAttributeInterface;
+use Drupal\Core\Template\HtmxAttribute;
+
+/**
+ * Collects HTMX attributes and headers and manages complex behaviors.
+ *
+ * An instance of this object is required to add HTMX behaviors to a render
+ * element.
+ *
+ * Methods to configure common behaviors are provided:
+ *
+ * @code
+ * $htmx = new Htmx();
+ * $node_url = Url::fromRoute(
+ *    route_name: entity.node.canonical',
+ *    route_parameters: ['node' => 123],
+ *  );
+ * $htmx->insert($node_url, 'div.example', 'article.page')
+ *
+ * $build = [
+ *    '#htmx' => $htmx,
+ *  ];
+ * @endcode
+ *
+ * Attributes may also be specified explicitly:
+ *
+ * @code
+ * $htmx = new Htmx();
+ * $form_url = Url::fromRoute(
+ *   route_name: 'config.export_single',
+ *   route_parameters: ['config_type' => $config_type, 'config_name' => $config_name],
+ * );
+ *
+ * $htmx->attributes()
+ *   ->post($form_url)
+ *   ->select('select[data-drupal-selector="edit-config-name"]')
+ *   ->target('select[data-drupal-selector="edit-config-name"]')
+ *   ->swap('outerHTML');
+ *
+ * $build = [
+ *   '#htmx' => $htmx,
+ * ];
+ * @endcode
+ *
+ * HTMX headers are added in a similar way.
+ *
+ * @code
+ * // Also update the browser URL.
+ * $push = Url::fromRoute(
+ *   route_name: 'config.export_single',
+ *   route_parameters: ['config_type' => $default_type, 'config_name' => $default_name],
+ * );
+ *
+ * $htmx = new Htmx();
+ * $htmx->headers()->pushUrl($push);
+ * $build = [
+ *   '#htmx' => $htmx,
+ * ];
+ * @endcode
+ *
+ * @see \Drupal\Core\Template\HtmxAttribute
+ * @see \Drupal\Core\Http\HtmxResponseHeaders
+ */
+class Htmx implements HtmxInterface {
+
+  /**
+   * Optional request operation.
+   *
+   * @var \Drupal\Core\Render\Hypermedia\Operations\HtmxRequestOperationInterface|null
+   */
+  protected HtmxRequestOperationInterface|null $requestOperation = NULL;
+
+  /**
+   * Additional operations that do not depend on a request.
+   *
+   * @var \Drupal\Core\Render\Hypermedia\Operations\HtmxOperationInterface[]
+   */
+  protected array $additionalOperations = [];
+
+  public function __construct(
+    public readonly HtmxAttribute $attributes = new HtmxAttribute(),
+    public readonly HtmxHeaderInterface $headers = new HtmxResponseHeaders(),
+  ) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function attributes(): HtmxAttribute {
+    return $this->attributes;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function headers(): HtmxHeaderInterface {
+    return $this->headers;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCombinedAttributes(array|HtmlAttributeInterface $attributes): HtmlAttributeInterface|array {
+    return AttributeHelper::mergeCollections($attributes, $this->attributes);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCombinedHeaders(array $headers): array {
+    return NestedArray::mergeDeep($headers, $this->headers->toArray());
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function merge(HtmxInterface $htmx): HtmxInterface {
+    $this->attributes->merge($htmx->attributes());
+    $this->headers->merge($htmx->headers());
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setRequestOperation(HtmxRequestOperationInterface $operation): HtmxInterface {
+    $this->requestOperation = $operation;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setAdditionalOperation(HtmxOperationInterface $operation): HtmxInterface {
+    if ($operation instanceof HtmxRequestOperationInterface) {
+      throw new \ValueError('Htmx::setRequestOperation() must be used to add HtmxRequestOperationInterface operations');
+    }
+    $this->additionalOperations[] = $operation;
+    return $this;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasOperations(): bool {
+    return $this->requestOperation instanceof HtmxRequestOperationInterface
+    || count($this->additionalOperations) !== 0;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processOperations(): void {
+    if ($this->hasOperations() === FALSE) {
+      return;
+    }
+    $operations = [];
+    if (count($this->additionalOperations) !== 0) {
+      $operations = $this->additionalOperations;
+    }
+    if ($this->requestOperation instanceof HtmxRequestOperationInterface) {
+      array_unshift($operations, $this->requestOperation);
+    }
+    foreach ($operations as $operation) {
+      $operation->setProperties($this);
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/HtmxInterface.php b/core/lib/Drupal/Core/Render/Hypermedia/HtmxInterface.php
new file mode 100644
index 0000000000000000000000000000000000000000..7fb99e66e93f730f31f0d1349c3ae26e3df58a9b
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/HtmxInterface.php
@@ -0,0 +1,103 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia;
+
+use Drupal\Core\Http\HtmxHeaderInterface;
+use Drupal\Core\Render\Hypermedia\Operations\HtmxOperationInterface;
+use Drupal\Core\Render\Hypermedia\Operations\HtmxRequestOperationInterface;
+use Drupal\Core\Template\HtmlAttributeInterface;
+use Drupal\Core\Template\HtmxAttribute;
+
+/**
+ * An interface for objects that manage HTMX behaviors.
+ */
+interface HtmxInterface {
+
+  /**
+   * Accessor for the HtmxAttribute.
+   *
+   * @return \Drupal\Core\Template\HtmxAttribute
+   *   The attributes object.
+   */
+  public function attributes(): HtmxAttribute;
+
+  /**
+   * Accessor for the headers, typically an instance of HtmxResponseHeader.
+   *
+   * @return \Drupal\Core\Http\HtmxHeaderInterface
+   *   The headers object.
+   */
+  public function headers(): HtmxHeaderInterface;
+
+  /**
+   * Merges this object's attributes with an array or collection of attributes.
+   *
+   * @param \Drupal\Core\Template\HtmlAttributeInterface|array $attributes
+   *   The data to merge.
+   *
+   * @return \Drupal\Core\Template\HtmlAttributeInterface|array
+   *   Returns the data in the form it was recieved.
+   */
+  public function getCombinedAttributes(HtmlAttributeInterface|array $attributes): HtmlAttributeInterface|array;
+
+  /**
+   * Produces a merged Drupal 'http_header' array.
+   *
+   * @param array $headers
+   *   A Drupal 'http_header' array to augment.
+   *
+   * @return array
+   *   This objects headers merged with the received headers.
+   */
+  public function getCombinedHeaders(array $headers): array;
+
+  /**
+   * Merges this objects data with another instance of HtmxInterface.
+   *
+   * @param \Drupal\Core\Render\Hypermedia\HtmxInterface $htmx
+   *   The source of additional data.
+   *
+   * @return \Drupal\Core\Render\Hypermedia\HtmxInterface
+   *   An instance with attributes and headers from both objects.
+   */
+  public function merge(HtmxInterface $htmx): HtmxInterface;
+
+  /**
+   * Sets the HTMX request operation for the element.
+   *
+   * @param \Drupal\Core\Render\Hypermedia\Operations\HtmxRequestOperationInterface $operation
+   *   The operation.
+   *
+   * @return \Drupal\Core\Render\Hypermedia\HtmxInterface
+   *   Returns self to enable chained methods.
+   */
+  public function setRequestOperation(HtmxRequestOperationInterface $operation): HtmxInterface;
+
+  /**
+   * Set an additional operation that don't use a request.
+   *
+   * These should be accumulated in a stack that is processed in
+   * ::processOperations.
+   *
+   * @param \Drupal\Core\Render\Hypermedia\Operations\HtmxOperationInterface $operation
+   *   The operation.
+   *
+   * @return \Drupal\Core\Render\Hypermedia\HtmxInterface
+   *   Returns self to enable chained methods.
+   */
+  public function setAdditionalOperation(HtmxOperationInterface $operation): HtmxInterface;
+
+  /**
+   * Checks for request or additional operations.
+   *
+   * @return bool
+   *   True if any operations are set.
+   */
+  public function hasOperations(): bool;
+
+  /**
+   * Step through all the operations, calling their ::setProperties method.
+   */
+  public function processOperations(): void;
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/HtmxResponseAttachmentsProcessor.php b/core/lib/Drupal/Core/Render/Hypermedia/HtmxResponseAttachmentsProcessor.php
new file mode 100644
index 0000000000000000000000000000000000000000..5c8881e7412f7fed01b2dfbcb67eff8aa7b03d9c
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/HtmxResponseAttachmentsProcessor.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Component\Utility\UrlHelper;
+use Drupal\Core\Asset\AttachedAssetsInterface;
+use Drupal\Core\Render\AttachmentsInterface;
+use Drupal\Core\Render\HtmlResponse;
+use Drupal\Core\Render\HtmlResponseAttachmentsProcessor;
+
+/**
+ * Prepares attachment for HTMX powered responses.
+ *
+ * Extends the HTML response processor encode attachment data.
+ *
+ * @see \Drupal\Core\EventSubscriber\HtmxResponseSubscriber
+ * @see \Drupal\Core\Render\HtmlResponseAttachmentsProcessor::processAttachments
+ * @see core/misc/htmx-behaviors.js
+ */
+class HtmxResponseAttachmentsProcessor extends HtmlResponseAttachmentsProcessor {
+
+  /**
+   * Json encoded string of event name and assets to be attached.
+   */
+  protected string $preparedAssetInfo;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function processAttachments(AttachmentsInterface $response): HtmlResponse {
+    $processed = parent::processAttachments($response);
+    if (!($processed instanceof HtmlResponse)) {
+      // Something has gone wrong. We sent an HtmlResponse that also
+      // implemented AttachmentInterface and should have received the same back.
+      throw new \TypeError("HtmlResponseAttachmentsProcessor::processAttachments should return an HtmlResponse.");
+    }
+    $processed->headers->set('HX-Trigger-After-Swap', $this->preparedAssetInfo);
+    return $processed;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function processAssetLibraries(AttachedAssetsInterface $assets, array $placeholders) {
+    $request = $this->requestStack->getCurrentRequest();
+    if ($request->headers->has('HX-Page-State')) {
+      $uncompressed = UrlHelper::uncompressQueryParameter($request->headers->get('HX-Page-State'));
+      $libraries = explode(',', $uncompressed);
+      $assets->setAlreadyLoadedLibraries($libraries);
+    }
+    $settings = [];
+    $variables = [];
+    $maintenance_mode = defined('MAINTENANCE_MODE') || \Drupal::state()->get('system.maintenance_mode');
+
+    // Print styles - if present.
+    if (isset($placeholders['styles'])) {
+      // Optimize CSS if necessary, but only during normal site operation.
+      $optimize_css = !$maintenance_mode && $this->config->get('css.preprocess');
+      $variables['styles'] = $this->cssCollectionRenderer->render($this->assetResolver->getCssAssets($assets, $optimize_css, $this->languageManager->getCurrentLanguage()));
+    }
+
+    // Copy and adjust parent::processAssetLibraries to adjust and
+    // remove drupalSettings in line with
+    // AjaxResponseAttachmentsProcessor::buildAttachmentsCommands
+    // Print scripts - if any are present.
+    if (isset($placeholders['scripts']) || isset($placeholders['scripts_bottom'])) {
+      // Optimize JS if necessary, but only during normal site operation.
+      $optimize_js = !$maintenance_mode && $this->config->get('js.preprocess');
+      [$js_assets_header, $js_assets_footer] = $this->assetResolver
+        ->getJsAssets($assets, $optimize_js, $this->languageManager->getCurrentLanguage());
+      $settingsHeader = $js_assets_header['drupalSettings'] ?? NULL;
+      $settingsFooter = $js_assets_footer['drupalSettings'] ?? NULL;
+      if (is_array($settingsHeader)) {
+        $settings = $js_assets_header['drupalSettings']['data'];
+        unset($js_assets_header['drupalSettings']);
+      }
+      if (is_array($settingsFooter)) {
+        $settings = $js_assets_footer['drupalSettings']['data'];
+        unset($js_assets_footer['drupalSettings']);
+      }
+      if (empty($settings)) {
+        $settings = $assets->getSettings();
+      }
+      $variables['scripts'] = $this->jsCollectionRenderer->render($js_assets_header);
+      $variables['scripts_bottom'] = $this->jsCollectionRenderer->render($js_assets_footer);
+      unset($settings['path']);
+      $variables['settings'] = $settings;
+    }
+    // Store the prepared asset data so that it can be added to the response.
+    $data = [
+      'htmxDrupalAssetsAttached' => [
+        'assets' => $variables,
+      ],
+    ];
+    $this->preparedAssetInfo = Json::encode($data);
+    // Restore assets for a standard page so that HTML state is preserved.
+    if (isset($settingsHeader) && is_array($settingsHeader)) {
+      $js_assets_header['drupalSettings'] = $settingsHeader;
+      $variables['scripts'] = $this->jsCollectionRenderer->render($js_assets_header);
+    }
+    if (isset($settingsFooter) && is_array($settingsFooter)) {
+      $js_assets_footer['drupalSettings'] = $settingsFooter;
+      $variables['scripts_bottom'] = $this->jsCollectionRenderer->render($js_assets_footer);
+    }
+    return $variables;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxOperationInterface.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxOperationInterface.php
new file mode 100644
index 0000000000000000000000000000000000000000..f2ebf5842fd126ad3655665005befc656524b76f
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxOperationInterface.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+use Drupal\Core\Render\Hypermedia\HtmxInterface;
+
+/**
+ * An HtmxOperation adds attributes or headers to an HTMX object.
+ */
+interface HtmxOperationInterface {
+
+  /**
+   * Add the necessary values to the Htmx object to implement the operation.
+   *
+   * @param \Drupal\Core\Render\Hypermedia\HtmxInterface $htmx
+   *   The Htmx object collecting the attributes and headers.
+   */
+  public function setProperties(HtmxInterface $htmx): void;
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestOperationInterface.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestOperationInterface.php
new file mode 100644
index 0000000000000000000000000000000000000000..e1a933724b5d8ad23a6047d70b248376feb36322
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestOperationInterface.php
@@ -0,0 +1,29 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+use Drupal\Core\Http\HttpMethod;
+use Drupal\Core\Url;
+
+/**
+ * This interface segments HTMX operations that perform and process a request.
+ *
+ * There can only be one HTMX request attribute and accompanying processing
+ * attributes on an HTML element.
+ */
+interface HtmxRequestOperationInterface extends HtmxOperationInterface {
+
+  /**
+   * Configures the method and url for the request.
+   *
+   * @param \Drupal\Core\Http\HttpMethod $method
+   *   The request method.
+   * @param \Drupal\Core\Url $url
+   *   The request URL.
+   *
+   * @return static
+   *   The instance using the trait.
+   */
+  public function setRequest(HttpMethod $method, Url $url): static;
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestTrait.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestTrait.php
new file mode 100644
index 0000000000000000000000000000000000000000..55c20710ea0766c01e2a2c81562cb7c1a4b64482
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxRequestTrait.php
@@ -0,0 +1,60 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+use Drupal\Core\Http\HttpMethod;
+use Drupal\Core\Render\Hypermedia\HtmxInterface;
+use Drupal\Core\Url;
+
+/**
+ * Provides reusable methods for HtmxRequestOperationInterface objects.
+ */
+trait HtmxRequestTrait {
+
+  /**
+   * The method to use for the request.
+   */
+  protected HttpMethod $method;
+
+  /**
+   * The url to use for the request.
+   */
+  protected Url $url;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setRequest(HttpMethod $method, Url $url): static {
+    $this->method = $method;
+    $this->url = $url;
+    return $this;
+  }
+
+  /**
+   * Map the stored parameters to HTMX attributes.
+   */
+  public function configureRequest(HtmxInterface $htmx): void {
+    switch ($this->method) {
+      case HttpMethod::Get:
+        $htmx->attributes()->get($this->url);
+        break;
+
+      case HttpMethod::Put:
+        $htmx->attributes()->put($this->url);
+        break;
+
+      case HttpMethod::Patch:
+        $htmx->attributes()->patch($this->url);
+        break;
+
+      case HttpMethod::Post:
+        $htmx->attributes()->post($this->url);
+        break;
+
+      case HttpMethod::Delete:
+        $htmx->attributes()->delete($this->url);
+        break;
+    }
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxSelectTrait.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxSelectTrait.php
new file mode 100644
index 0000000000000000000000000000000000000000..1ce1e2f88d3fbbeb6487477ae3dc35c0d77adeac
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxSelectTrait.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+/**
+ * Provides reusable parameters and methods to support the use of hx-select.
+ *
+ * @see https://htmx.org/attributes/hx-select
+ */
+trait HtmxSelectTrait {
+
+
+  /**
+   * Specifies the markup to select from the returned request.
+   *
+   * A CSS query selector of the element or elements to select from the
+   * response.
+   */
+  protected string $select;
+
+  /**
+   * Setter method for $select.
+   *
+   * @param string $value
+   *   The value to set.
+   *
+   * @return static
+   *   The instance using the trait.
+   */
+  public function select(string $value): static {
+    $this->select = $value;
+    return $this;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxTargetTrait.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxTargetTrait.php
new file mode 100644
index 0000000000000000000000000000000000000000..d7997aa346430f76d6d9fe6a732599b00372bb1e
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/HtmxTargetTrait.php
@@ -0,0 +1,54 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+/**
+ * Provides reusable parameters and methods to support the use of hx-target.
+ *
+ * @see https://htmx.org/attributes/hx-target
+ */
+trait HtmxTargetTrait {
+
+  /**
+   * Specifies the element to target for replacement.
+   *
+   * The value is one of the following:
+   * - A CSS query selector of the element to target.
+   * - 'this'
+   *   Indicates that element receiving the htmx attributes is the target.
+   * - 'closest <CSS selector>'
+   *    Finds the closest ancestor element or itself, that matches the given
+   *    CSS selector (e.g. 'closest tr' will target the closest table row to
+   *    the element).
+   * - 'find <CSS selector>'
+   *    Finds the first child descendant element that matches the given CSS
+   *    selector.
+   * - 'next'
+   *    Resolves to element.nextElementSibling
+   * - 'next <CSS selector>'
+   *    Scans the DOM forward for the first element that matches the given CSS
+   *    selector. (e.g. 'next .error' will target the closest following sibling
+   *    element with the error class)
+   * - 'previous' which resolves to element.previousElementSibling
+   * - 'previous <CSS selector>'
+   *    Scan the DOM backwards for the first element that matches the given CSS
+   *    selector. (e.g. `previous .error` will target the closest previous
+   *    sibling with the error class)
+   */
+  protected string $target;
+
+  /**
+   * Setter method for $target.
+   *
+   * @param string $value
+   *   The value to set.
+   *
+   * @return static
+   *   The instance using the trait.
+   */
+  public function target(string $value): static {
+    $this->target = $value;
+    return $this;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/Insert.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/Insert.php
new file mode 100644
index 0000000000000000000000000000000000000000..11602ba36ed2993d3b12ff02fc486409cf9ca116
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/Insert.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+use Drupal\Core\Render\Hypermedia\HtmxInterface;
+
+/**
+ * Inserts the selected element as the last child of the target element.
+ */
+class Insert implements HtmxRequestOperationInterface {
+  use HtmxRequestTrait;
+  use HtmxSelectTrait;
+  use HtmxTargetTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setProperties(HtmxInterface $htmx): void {
+    $this->configureRequest($htmx);
+    $htmx->attributes()->select($this->select);
+    $htmx->attributes()->target($this->target);
+    $htmx->attributes()->swap('beforeend');
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Render/Hypermedia/Operations/Replace.php b/core/lib/Drupal/Core/Render/Hypermedia/Operations/Replace.php
new file mode 100644
index 0000000000000000000000000000000000000000..b8f46ed93ad62a23f7baf903ec833691202c1ed1
--- /dev/null
+++ b/core/lib/Drupal/Core/Render/Hypermedia/Operations/Replace.php
@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\Core\Render\Hypermedia\Operations;
+
+use Drupal\Core\Render\Hypermedia\HtmxInterface;
+
+/**
+ * Replaces the target element with the element.
+ */
+class Replace implements HtmxRequestOperationInterface {
+  use HtmxRequestTrait;
+  use HtmxSelectTrait;
+  use HtmxTargetTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setProperties(HtmxInterface $htmx): void {
+    $this->configureRequest($htmx);
+    $htmx->attributes()->select($this->select);
+    $htmx->attributes()->target($this->target);
+    $htmx->attributes()->swap('outerHTML');
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index 77a56689219df28092b462afd8e950b68188df4f..104464dba835d5433daa2643bd6542458f66cc27 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -4,8 +4,6 @@
 
 use Drupal\Component\Render\PlainTextOutput;
 use Drupal\Component\Render\MarkupInterface;
-use Drupal\Component\Utility\NestedArray;
-use Drupal\Core\Serialization\Attribute\JsonSchema;
 
 /**
  * Collects, sanitizes, and renders HTML attributes.
@@ -67,14 +65,16 @@
  * @see \Drupal\Component\Render\PlainTextOutput::renderFromHtml()
  * @see \Drupal\Component\Utility\UrlHelper::stripDangerousProtocols()
  */
-class Attribute implements \ArrayAccess, \IteratorAggregate, MarkupInterface {
+class Attribute implements HtmlAttributeInterface, \ArrayAccess {
+
+  use HtmlAttributeTrait;
 
   /**
    * Stores the attribute data.
    *
    * @var \Drupal\Core\Template\AttributeValueBase[]
    */
-  protected $storage = [];
+  protected array $storage = [];
 
   /**
    * Constructs a \Drupal\Core\Template\Attribute object.
@@ -91,7 +91,7 @@ public function __construct($attributes = []) {
   /**
    * {@inheritdoc}
    */
-  public function offsetGet($name): mixed {
+  public function offsetGet($name): ?AttributeValueBase {
     if (isset($this->storage[$name])) {
       return $this->storage[$name];
     }
@@ -123,7 +123,7 @@ public function offsetSet($name, $value): void {
    * @return \Drupal\Core\Template\AttributeValueBase
    *   An AttributeValueBase representation of the attribute's value.
    */
-  protected function createAttributeValue($name, $value) {
+  protected function createAttributeValue($name, $value): AttributeValueBase {
     // If the value is already an AttributeValueBase object,
     // return a new instance of the same class, but with the new name.
     if ($value instanceof AttributeValueBase) {
@@ -180,7 +180,7 @@ public function offsetExists($name): bool {
    *
    * @return $this
    */
-  public function addClass(...$args) {
+  public function addClass(...$args): self {
     if ($args) {
       $classes = [];
       foreach ($args as $arg) {
@@ -215,7 +215,7 @@ public function addClass(...$args) {
    *
    * @return $this
    */
-  public function setAttribute($attribute, $value) {
+  public function setAttribute($attribute, $value): self {
     $this->offsetSet($attribute, $value);
 
     return $this;
@@ -230,7 +230,7 @@ public function setAttribute($attribute, $value) {
    * @return bool
    *   Returns TRUE if the attribute exists, or FALSE otherwise.
    */
-  public function hasAttribute($name) {
+  public function hasAttribute($name): bool {
     return array_key_exists($name, $this->storage);
   }
 
@@ -242,7 +242,7 @@ public function hasAttribute($name) {
    *
    * @return $this
    */
-  public function removeAttribute(...$args) {
+  public function removeAttribute(...$args): self {
     foreach ($args as $arg) {
       // Support arrays or multiple arguments.
       if (is_array($arg)) {
@@ -266,7 +266,7 @@ public function removeAttribute(...$args) {
    *
    * @return $this
    */
-  public function removeClass(...$args) {
+  public function removeClass(...$args): self {
     // With no class attribute, there is no need to remove.
     if (isset($this->storage['class']) && $this->storage['class'] instanceof AttributeArray) {
       $classes = [];
@@ -291,12 +291,12 @@ public function removeClass(...$args) {
    *
    * This method is implemented to take precedence over hasClass() for Twig 2.0.
    *
-   * @return \Drupal\Core\Template\AttributeValueBase
+   * @return \Drupal\Core\Template\AttributeArray
    *   The class attribute value if set.
    *
    * @see twig_get_attribute()
    */
-  public function getClass() {
+  public function getClass(): AttributeArray {
     return $this->offsetGet('class');
   }
 
@@ -309,7 +309,7 @@ public function getClass() {
    * @return bool
    *   Returns TRUE if the class exists, or FALSE otherwise.
    */
-  public function hasClass($class) {
+  public function hasClass($class): bool {
     if (isset($this->storage['class']) && $this->storage['class'] instanceof AttributeArray) {
       return in_array($class, $this->storage['class']->value());
     }
@@ -318,37 +318,6 @@ public function hasClass($class) {
     }
   }
 
-  /**
-   * Implements the magic __toString() method.
-   */
-  #[JsonSchema(['type' => 'string', 'description' => 'Rendered HTML element attributes'])]
-  public function __toString() {
-    $return = '';
-    /** @var \Drupal\Core\Template\AttributeValueBase $value */
-    foreach ($this->storage as $value) {
-      $rendered = $value->render();
-      if ($rendered) {
-        $return .= ' ' . $rendered;
-      }
-    }
-    return $return;
-  }
-
-  /**
-   * Returns all storage elements as an array.
-   *
-   * @return array
-   *   An associative array of attributes.
-   */
-  public function toArray() {
-    $return = [];
-    foreach ($this->storage as $name => $value) {
-      $return[$name] = $value->value();
-    }
-
-    return $return;
-  }
-
   /**
    * Implements the magic __clone() method.
    */
@@ -366,36 +335,17 @@ public function getIterator(): \ArrayIterator {
   }
 
   /**
-   * Returns the whole array.
-   */
-  public function storage() {
-    return $this->storage;
-  }
-
-  /**
-   * Returns a representation of the object for use in JSON serialization.
-   *
-   * @return string
-   *   The safe string content.
+   * {@inheritdoc}
    */
-  public function jsonSerialize(): string {
-    return (string) $this;
+  public function count(): int {
+    return count($this->storage);
   }
 
   /**
-   * Merges an Attribute object into the current storage.
-   *
-   * @param \Drupal\Core\Template\Attribute $collection
-   *   The Attribute object to merge.
-   *
-   * @return $this
+   * Returns the whole array.
    */
-  public function merge(Attribute $collection) {
-    $merged_attributes = NestedArray::mergeDeep($this->toArray(), $collection->toArray());
-    foreach ($merged_attributes as $name => $value) {
-      $this->storage[$name] = $this->createAttributeValue($name, $value);
-    }
-    return $this;
+  public function storage(): array {
+    return $this->storage;
   }
 
 }
diff --git a/core/lib/Drupal/Core/Template/AttributeHelper.php b/core/lib/Drupal/Core/Template/AttributeHelper.php
index c4b0fbfa1e5448a7277aa465dc39ff5843dc1d3d..264148f68603a408e6059400fc098767bba5d51f 100644
--- a/core/lib/Drupal/Core/Template/AttributeHelper.php
+++ b/core/lib/Drupal/Core/Template/AttributeHelper.php
@@ -22,7 +22,7 @@ private function __construct() {
    *
    * @param string $name
    *   The name of the attribute to check for.
-   * @param \Drupal\Core\Template\Attribute|array $collection
+   * @param HtmlAttributeInterface|array $collection
    *   An Attribute object or an array of attributes.
    *
    * @return bool
@@ -32,7 +32,7 @@ private function __construct() {
    *   When the input $collection is neither an Attribute object nor an array.
    */
   public static function attributeExists($name, $collection) {
-    if ($collection instanceof Attribute) {
+    if ($collection instanceof HtmlAttributeInterface) {
       return $collection->hasAttribute($name);
     }
     elseif (is_array($collection)) {
@@ -44,32 +44,33 @@ public static function attributeExists($name, $collection) {
   /**
    * Merges two attribute collections.
    *
-   * @param \Drupal\Core\Template\Attribute|array $a
+   * @param HtmlAttributeInterface|array $a
    *   First Attribute object or array to merge. The returned value type will
    *   be the same as the type of this argument.
-   * @param \Drupal\Core\Template\Attribute|array $b
+   * @param HtmlAttributeInterface|array $b
    *   Second Attribute object or array to merge.
    *
    * @return \Drupal\Core\Template\Attribute|array
-   *   The merged attributes, as an Attribute object or an array.
+   *   The merged attributes in the form of the first argument.
    *
    * @throws \InvalidArgumentException
    *   If at least one collection argument is neither an Attribute object nor an
    *   array.
    */
   public static function mergeCollections($a, $b) {
-    if (!($a instanceof Attribute || is_array($a)) || !($b instanceof Attribute || is_array($b))) {
+    if (!($a instanceof HtmlAttributeInterface || is_array($a)) || !($b instanceof HtmlAttributeInterface || is_array($b))) {
       throw new \InvalidArgumentException('Invalid collection argument');
     }
     // If both collections are arrays, just merge them.
     if (is_array($a) && is_array($b)) {
       return NestedArray::mergeDeep($a, $b);
     }
-    // If at least one collections is an Attribute object, merge through
-    // Attribute::merge.
+    // Merge through Attribute::merge.
     $merge_a = $a instanceof Attribute ? $a : new Attribute($a);
     $merge_b = $b instanceof Attribute ? $b : new Attribute($b);
     $merge_a->merge($merge_b);
+    // If we started with an Attribute, return an Attribute.
+    // If we started with an array, return an array.
     return $a instanceof Attribute ? $merge_a : $merge_a->toArray();
   }
 
diff --git a/core/lib/Drupal/Core/Template/AttributeJson.php b/core/lib/Drupal/Core/Template/AttributeJson.php
new file mode 100644
index 0000000000000000000000000000000000000000..3b0204b371db27b8b0620795d78432279c91e0e4
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/AttributeJson.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Drupal\Core\Template;
+
+use Drupal\Component\Utility\Xss;
+
+/**
+ * Represents an attribute containing JSON formatted data.
+ */
+class AttributeJson extends AttributeValueBase {
+
+  const RENDER_EMPTY_ATTRIBUTE = FALSE;
+
+  /**
+   * Encode the array as JSON.
+   *
+   * @return string
+   *   The JSON encoded array or empty string on failure.
+   */
+  public function __toString() {
+    $value = $this->value();
+    $value = is_array($value) ? $value : [$value];
+    // Escape the values.
+    $data = [];
+    foreach ($value as $key => $item) {
+      $data[Xss::filter($key)] = is_string($item) ? Xss::filter($item) : $item;
+    }
+    $string = json_encode($data, JSON_FORCE_OBJECT | JSON_NUMERIC_CHECK);
+    return $string ?: '';
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/AttributeString.php b/core/lib/Drupal/Core/Template/AttributeString.php
index bce832e374a01bf44b2b98445117284693b22a4f..27f6cfc0d7c1edf0fdb57354f9b8f2c4a6e30576 100644
--- a/core/lib/Drupal/Core/Template/AttributeString.php
+++ b/core/lib/Drupal/Core/Template/AttributeString.php
@@ -2,7 +2,7 @@
 
 namespace Drupal\Core\Template;
 
-use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\Xss;
 
 /**
  * A class that represents most standard HTML attributes.
@@ -25,7 +25,7 @@ class AttributeString extends AttributeValueBase {
    * Implements the magic __toString() method.
    */
   public function __toString() {
-    return Html::escape((string) $this->value);
+    return Xss::filter((string) $this->value);
   }
 
 }
diff --git a/core/lib/Drupal/Core/Template/AttributeValueBase.php b/core/lib/Drupal/Core/Template/AttributeValueBase.php
index 35ef176b14563962dd07799ace6fc2943da58ed8..f33455092f97cd7f7f0fb231b30097599d8f6edf 100644
--- a/core/lib/Drupal/Core/Template/AttributeValueBase.php
+++ b/core/lib/Drupal/Core/Template/AttributeValueBase.php
@@ -7,6 +7,7 @@
 /**
  * Defines the base class for an attribute type.
  *
+ * @see https://html.spec.whatwg.org/#attributes-2
  * @see \Drupal\Core\Template\Attribute
  */
 abstract class AttributeValueBase {
@@ -46,15 +47,19 @@ public function __construct($name, $value) {
    * While __toString only returns the value in a string form, render()
    * contains the name of the attribute as well.
    *
-   * @return string|null
+   * @return string
    *   The string representation of the attribute.
    */
   public function render() {
     $value = (string) $this;
+    $singleQuote = str_contains($value, '"');
     if (isset($this->value) && static::RENDER_EMPTY_ATTRIBUTE || !empty($value)) {
-      return Html::escape($this->name) . '="' . $value . '"';
+      // Flips the attribute quotes between single and double-quoted syntax.
+      $rendered = Html::escape($this->name);
+      $rendered .= $singleQuote ? "='" . $value . "'" : '="' . $value . '"';
+      return $rendered;
     }
-    return NULL;
+    return '';
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Template/ComponentsTwigExtension.php b/core/lib/Drupal/Core/Template/ComponentsTwigExtension.php
index 5ff5c7e94b6bac87ddb3ae5746a6eb0ada171baa..88269ada867052cd36c5eefc9d17aaaacb5b4655 100644
--- a/core/lib/Drupal/Core/Template/ComponentsTwigExtension.php
+++ b/core/lib/Drupal/Core/Template/ComponentsTwigExtension.php
@@ -83,7 +83,7 @@ protected function mergeAdditionalRenderContext(Component $component, array $con
     }
     // If there is an "attributes" property, merge the additional attributes
     // into it if possible.
-    elseif ($context['attributes'] instanceof Attribute) {
+    elseif ($context['attributes'] instanceof HtmlAttributeInterface) {
       $context['attributes']->merge(new Attribute($component_attributes));
     }
     return $context;
diff --git a/core/lib/Drupal/Core/Template/HtmlAttributeInterface.php b/core/lib/Drupal/Core/Template/HtmlAttributeInterface.php
new file mode 100644
index 0000000000000000000000000000000000000000..3d0954bfca04cca9785c0926a1d8c74f2c49add4
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/HtmlAttributeInterface.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Drupal\Core\Template;
+
+use Drupal\Component\Render\MarkupInterface;
+
+/**
+ * An interface for classes that manage HTML Attributes.
+ *
+ * @extends \IteratorAggregate<string, \Drupal\Core\Template\AttributeValueBase>
+ */
+interface HtmlAttributeInterface extends \Countable, \IteratorAggregate, MarkupInterface {
+
+  /**
+   * Checks if the storage has an attribute with the given name.
+   *
+   * @param string $name
+   *   The name of the attribute to check for.
+   *
+   * @return bool
+   *   Returns TRUE if the attribute exists, or FALSE otherwise.
+   */
+  public function hasAttribute($name): bool;
+
+  /**
+   * Returns all storage elements as an array.
+   *
+   * @return mixed[]
+   *   An associative array of attributes.
+   */
+  public function toArray(): array;
+
+  /**
+   * Merges an Attribute object into the current storage.
+   *
+   * @param HtmlAttributeInterface $collection
+   *   The Attribute object to merge.
+   *
+   * @return $this
+   */
+  public function merge(HtmlAttributeInterface $collection): HtmlAttributeInterface;
+
+}
diff --git a/core/lib/Drupal/Core/Template/HtmlAttributeTrait.php b/core/lib/Drupal/Core/Template/HtmlAttributeTrait.php
new file mode 100644
index 0000000000000000000000000000000000000000..2efe43c776e662fd993a26cae388c4b95ee37cc6
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/HtmlAttributeTrait.php
@@ -0,0 +1,81 @@
+<?php
+
+namespace Drupal\Core\Template;
+
+use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Serialization\Attribute\JsonSchema;
+
+/**
+ * Provides a shared implementation of several HtmlAttribute methods.
+ *
+ * Methods that depend on the storage method are omitted and should be
+ * implemented directly.
+ */
+trait HtmlAttributeTrait {
+
+  /**
+   * Implements the magic __toString() method.
+   */
+  #[JsonSchema(['type' => 'string', 'description' => 'Rendered HTML element attributes'])]
+  public function __toString() {
+    $return = '';
+    /** @var \Drupal\Core\Template\AttributeValueBase $value */
+    foreach ($this->storage as $value) {
+      $rendered = $value->render();
+      if ($rendered) {
+        $return .= ' ' . $rendered;
+      }
+    }
+    return $return;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function toArray(): array {
+    $return = [];
+    foreach ($this->storage as $name => $value) {
+      $return[$name] = $value->value();
+    }
+
+    return $return;
+  }
+
+  /**
+   * Returns a representation of the object for use in JSON serialization.
+   *
+   * @return string
+   *   The safe string content.
+   */
+  public function jsonSerialize(): string {
+    return (string) $this;
+  }
+
+  /**
+   * Merges an Attribute object into the current storage.
+   *
+   * On name matches, incoming AttributeArrays run through
+   * NestedArray::mergeDeep.  Other Attribute types replace a matching name.
+   * This is an equivalent behavior to converting all values arrays and
+   * running NestedArray::mergeDeep on the arrays which preserves the
+   * types of the values.
+   *
+   * @param HtmlAttributeInterface $collection
+   *   The Attribute object to merge.
+   *
+   * @return $this
+   */
+  public function merge(HtmlAttributeInterface $collection): self {
+    foreach ($collection as $name => $value) {
+      if (isset($this->storage[$name]) && $value instanceof AttributeArray) {
+        $merged_attributes = NestedArray::mergeDeep($this->storage[$name]->value(), $value->value());
+        $this->storage[$name] = new AttributeArray($name, $merged_attributes);
+      }
+      else {
+        $this->storage[$name] = $value;
+      }
+    }
+    return $this;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/HtmxAttribute.php b/core/lib/Drupal/Core/Template/HtmxAttribute.php
new file mode 100644
index 0000000000000000000000000000000000000000..3d79403e57e159e4cf43ec70bfede6907383a8ab
--- /dev/null
+++ b/core/lib/Drupal/Core/Template/HtmxAttribute.php
@@ -0,0 +1,769 @@
+<?php
+
+namespace Drupal\Core\Template;
+
+use Drupal\Core\Url;
+use Symfony\Component\Serializer\NameConverter\CamelCaseToSnakeCaseNameConverter;
+
+/**
+ * Collects, sanitizes, and renders attributes for HTMX integration.
+ *
+ * This object is composed into \Drupal\Core\Ajax\Htmx. The most common usage
+ * will be to access it as a property there.
+ *
+ * There are times when this class is needed directly because a portion of
+ * HTML is being managed directly, such as a prefix
+ * element.
+ *
+ * @code
+ * $attributes = new Attribute(['id' => 'edit-export-wrapper']);
+ * $export_htmx_attributes = new HtmxAttribute();
+ * $export_htmx_attributes->swapOob('outerHTML:#edit-export-wrapper');
+ * $attributes = $attributes->merge($export_htmx_attributes);
+ * $form['export']['#prefix'] = '<div  ' . $attributes . '>';
+ * @endcode
+ *
+ * @see \Drupal\Core\Render\Hypermedia\Htmx
+ * @see https://htmx.org/reference/
+ */
+class HtmxAttribute implements HtmlAttributeInterface {
+
+  use HtmlAttributeTrait;
+
+  /**
+   * Stores the attribute data.
+   *
+   * @var \Drupal\Core\Template\AttributeValueBase[]
+   */
+  protected array $storage = [];
+
+  /* ***** Internal utility methods ***** */
+
+  /**
+   * Utility method to transform camelCase strings to kebab-case strings.
+   *
+   * Passes kebab-case strings through without any transformation.
+   *
+   * @param string $identifier
+   *   The string to verify or transform.
+   *
+   * @return string
+   *   The original or transformed string.
+   */
+  protected function insureKebabCase(string $identifier): string {
+    // Check for existing kebab case.
+    $kebabParts = explode('-', $identifier);
+    // If the number of lower case parts matches the number of parts, then
+    // all the parts are lower case.
+    $isKebab = count($kebabParts) === count(array_filter($kebabParts, function ($part) {
+      return preg_match('#^[[:lower:]]+$#', $part) === 1;
+    }));
+    if ($isKebab) {
+      return $identifier;
+    }
+
+    $converter = new CamelCaseToSnakeCaseNameConverter();
+    $snakeCase = $converter->normalize($identifier);
+    return preg_replace('#[_:]#', '-', $snakeCase);
+  }
+
+  /**
+   * Utility method to create and store a string value as an attribute.
+   *
+   * @param string $id
+   *   The HTMX attribute id.
+   * @param string $value
+   *   The attribute value.
+   */
+  protected function createStringAttribute(string $id, string $value): void {
+    $key = 'data-hx-' . $id;
+    $attribute = new AttributeString($key, $value);
+    $this->storage[$key] = $attribute;
+  }
+
+  /**
+   * Utility method to create and store a boolean value as an attribute.
+   *
+   * @param string $id
+   *   The HTMX attribute id.
+   * @param bool $value
+   *   The attribute value.
+   */
+  protected function createBooleanAttribute(string $id, bool $value): void {
+    $key = 'data-hx-' . $id;
+    $attribute = new AttributeBoolean($key, $value);
+    $this->storage[$key] = $attribute;
+
+  }
+
+  /**
+   * Utility method to create and store an array as an attribute.
+   *
+   * @param string $id
+   *   The HTMX attribute id.
+   * @param array{string, string} $value
+   *   The attribute values.
+   */
+  protected function createJsonAttribute(string $id, array $value): void {
+    $key = 'data-hx-' . $id;
+    $attribute = new AttributeJson($key, $value);
+    $this->storage[$key] = $attribute;
+  }
+
+  /* ***** HtmxAttribute methods ***** */
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasAttribute($name): bool {
+    return array_key_exists($name, $this->storage);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getIterator(): \ArrayIterator {
+    return new \ArrayIterator($this->storage);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function count(): int {
+    return count($this->storage);
+  }
+
+  /* ***** Request attributes ***** */
+
+  /**
+   * Issues a GET request to the specified URL.
+   *
+   * @param \Drupal\Core\Url $url
+   *   The URL for the GET request.
+   *
+   * @return HtmxAttribute
+   *   returns self so that attribute methods may be chained.
+   *
+   * @see https://htmx.org/attributes/hx-get/
+   */
+  public function get(Url $url): HtmxAttribute {
+    $this->createStringAttribute('get', $url->toString());
+    return $this;
+  }
+
+  /**
+   * Issues a POST request to the specified URL.
+   *
+   * @param \Drupal\Core\Url $url
+   *   The URL for the POST request.
+   *
+   * @return HtmxAttribute
+   *   returns self so that attribute methods may be chained.
+   *
+   * @see https://htmx.org/attributes/hx-post/
+   */
+  public function post(Url $url): HtmxAttribute {
+    $this->createStringAttribute('post', $url->toString());
+    return $this;
+  }
+
+  /**
+   * Issues a PUT request to the specified URL.
+   *
+   * @param \Drupal\Core\Url $url
+   *   The URL for the PUT request.
+   *
+   * @return HtmxAttribute
+   *   returns self so that attribute methods may be chained.
+   *
+   * @see https://htmx.org/attributes/hx-put/
+   */
+  public function put(Url $url): HtmxAttribute {
+    $this->createStringAttribute('put', $url->toString());
+    return $this;
+  }
+
+  /**
+   * Issues a PATCH request to the specified URL.
+   *
+   * @param \Drupal\Core\Url $url
+   *   The URL for the PATCH request.
+   *
+   * @return HtmxAttribute
+   *   returns self so that attribute methods may be chained.
+   *
+   * @see https://htmx.org/attributes/hx-patch/
+   */
+  public function patch(Url $url): HtmxAttribute {
+    $this->createStringAttribute('patch', $url->toString());
+    return $this;
+  }
+
+  /**
+   * Issues a DELETE request to the specified URL.
+   *
+   * @param \Drupal\Core\Url $url
+   *   The URL for the DELETE request.
+   *
+   * @return HtmxAttribute
+   *   returns self so that attribute methods may be chained.
+   *
+   * @see https://htmx.org/attributes/hx-delete/
+   */
+  public function delete(Url $url): HtmxAttribute {
+    $this->createStringAttribute('delete', $url->toString());
+    return $this;
+  }
+
+  /* ***** Remaining HTMX 'core' attributes ***** */
+
+  /**
+   * Handle events with inline scripts on elements.
+   *
+   * @param string $event
+   *   An event in either camelCase or kebab-case.
+   * @param string $action
+   *   The action to take when the event occurs.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-on/
+   */
+  public function on(string $event, string $action): HtmxAttribute {
+    // Special case: the `::EventName` shorthand for `htmx:EventName`.
+    // Remove one leading `:` so that our final attribute is
+    // `data-hx--event-name` rather than `data-hx---event-name`.
+    $event = preg_replace('#^::#', ':', $event);
+    $formattedEvent = 'on-' . $this->insureKebabCase($event);
+    $this->createStringAttribute($formattedEvent, $action);
+    return $this;
+  }
+
+  /**
+   * Control URLs in browser history.
+   *
+   * Use a boolean when this attribute is added along with ::get
+   * - true: pushes the fetched URL into history.
+   * - false: disables pushing the fetched URL if it would otherwise be pushed
+   *   due to inheritance or hx-boost.
+   *
+   * Use a URL to cause a push into the location bar. This may be relative or
+   * absolute, as per history.pushState()
+   *
+   * @param bool|\Drupal\Core\Url $value
+   *   Use a Url object or a boolean, depending on use case.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-push-url/
+   */
+  public function pushUrl(bool|Url $value): HtmxAttribute {
+    if ($value instanceof Url) {
+      $this->createStringAttribute('push-url', $value->toString());
+    }
+    else {
+      $this->createStringAttribute('push-url', $value ? 'true' : 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * Select content to swap in from a response.
+   *
+   * Uses the selector to select elements from the response.
+   *
+   * @param string $selector
+   *   A CSS query selector.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-select/
+   */
+  public function select(string $selector): HtmxAttribute {
+    $this->createStringAttribute('select', $selector);
+    return $this;
+  }
+
+  /**
+   * Select content for an out-of-band swap from a response.
+   *
+   * Each value in the comma separated list of values can specify any valid
+   * hx-swap strategy by separating the selector and the swap strategy with a
+   * colon, such as #alert:afterbegin.
+   *
+   * @param string $selectors
+   *   A comma separated list of elements to be swapped out of band.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-select-oob/
+   */
+  public function selectOob(string $selectors): HtmxAttribute {
+    $this->createStringAttribute('select-oob', $selectors);
+    return $this;
+  }
+
+  /**
+   * Controls how content will swap in.
+   *
+   * The hx-swap attribute allows you to specify how the response will be
+   * swapped in relative to the target of an AJAX request.
+   *
+   * @param string $strategy
+   *   A comma separated list of elements to be swapped out of band.
+   * @param bool $ignoreTitle
+   *   Instruct HTMX not to swap in the page title from the request.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-swap/
+   */
+  public function swap(string $strategy, bool $ignoreTitle = TRUE): HtmxAttribute {
+    // HTMX defaults this behavior to FALSE, that is it replaces page title.
+    // We believe our most common use case is to not change the title.
+    if ($ignoreTitle) {
+      $strategy .= '  ignoreTitle:true';
+    }
+    $this->createStringAttribute('swap', $strategy);
+    return $this;
+  }
+
+  /**
+   * Designate content in a response for an out-of-band swap.
+   *
+   * The hx-swap-oob attribute allows you to specify that some content in a
+   * response should be swapped into the DOM somewhere other than the target,
+   * that is “Out of Band”. This allows you to piggyback updates to other
+   * element updates on a response.
+   *
+   * @param string $value
+   *   A comma separated list of elements to be swapped out of band.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-swap-oob/
+   */
+  public function swapOob(true|string $value): HtmxAttribute {
+    if ($value === TRUE) {
+      $this->createStringAttribute('swap-oob', 'true');
+    }
+    else {
+      $this->createStringAttribute('swap-oob', $value);
+    }
+    return $this;
+  }
+
+  /**
+   * Specifies the target element to receive  the incoming markup.
+   *
+   * The hx-target attribute allows you to target a different element for
+   * swapping than the one issuing the AJAX request. There are a variety
+   * of target string syntaxes.  See the URL below for details.
+   *
+   * @param string $target
+   *   The target descriptor.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-target/
+   */
+  public function target(string $target): HtmxAttribute {
+    $this->createStringAttribute('target', $target);
+    return $this;
+  }
+
+  /**
+   * Specifies what triggers a request.
+   *
+   * Used with an HTMX request attribute. Allows:
+   * - An event name (e.g. “click” or “my-custom-event”) followed by an event
+   *   filter and a set of event modifiers
+   * - A polling definition of the form every <timing declaration>
+   * - A comma-separated list of such events.
+   *
+   * @param string $triggerDefinition
+   *   The trigger definition.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-trigger/
+   */
+  public function trigger(string $triggerDefinition): HtmxAttribute {
+    $this->createStringAttribute('trigger', $triggerDefinition);
+    return $this;
+  }
+
+  /**
+   * Add to the parameters that will be submitted with an HTMX request.
+   *
+   * The value of this attribute is a list of name-expression values
+   * which will be converted to JSON (JavaScript Object Notation) format.
+   *
+   * @param array<string, string> $values
+   *   The values in an array of 'name' => 'value' pairs.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-trigger/
+   */
+  public function vals(array $values): HtmxAttribute {
+    $this->createJsonAttribute('vals', $values);
+    return $this;
+  }
+
+  /* ***** Remaining HTMX 'core' attributes ***** */
+
+  /**
+   * Add progressive enhancement for links and forms.
+   *
+   * The hx-boost attribute allows you to “boost” normal anchors and form tags
+   * to use AJAX instead. This has the nice fallback that, if the user does not
+   * have javascript enabled, the site will continue to work.
+   *
+   * @param bool $value
+   *   Should the element and its descendants be "boosted"?
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-boost/
+   */
+  public function boost(bool $value): HtmxAttribute {
+    if ($value === TRUE) {
+      $this->createStringAttribute('boost', 'true');
+    }
+    else {
+      $this->createStringAttribute('boost', 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * Shows a confirm() dialog before issuing a request.
+   *
+   * @param string $message
+   *   The user facing message.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-confirm/
+   */
+  public function confirm(string $message): HtmxAttribute {
+    $this->createStringAttribute('confirm', $message);
+    return $this;
+  }
+
+  /**
+   * Disables HTMX processing for the given node and any descendants.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-disable/
+   */
+  public function disable(): HtmxAttribute {
+    $this->createBooleanAttribute('disable', TRUE);
+    return $this;
+  }
+
+  /**
+   * Adds the disabled attribute to the specified elements during a request.
+   *
+   * The descriptor syntax is the same as hx-target. See the documentation
+   * link below for more details.
+   *
+   * @param string $descriptor
+   *   The attribute value.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-disabled-elt/
+   */
+  public function disabledElements(string $descriptor): HtmxAttribute {
+    $this->createStringAttribute('disabled-elt', $descriptor);
+    return $this;
+  }
+
+  /**
+   * Control and disable automatic HTMX attribute inheritance for child nodes.
+   *
+   * @param string $names
+   *   The attribute names to disinherit or * for all.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-disinherit/
+   */
+  public function disinherit(string $names): HtmxAttribute {
+    $this->createStringAttribute('disinherit', $names);
+    return $this;
+  }
+
+  /**
+   * Changes the request encoding type.
+   *
+   * @param string $method
+   *   The encoding method.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-encoding/
+   */
+  public function encoding(string $method = 'multipart/form-data'): HtmxAttribute {
+    $this->createStringAttribute('encoding', $method);
+    return $this;
+  }
+
+  /**
+   * Enables HTMX extensions for an element and descendants.
+   *
+   * @param string $names
+   *   An extension name, or a comma separated list of names.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-ext/
+   */
+  public function ext(string $names): HtmxAttribute {
+    $this->createStringAttribute('ext', $names);
+    return $this;
+  }
+
+  /**
+   * Add to the headers that will be submitted with an HTMX request.
+   *
+   * @param array<string, string> $headerValues
+   *   The header values as name => value.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-headers/
+   */
+  public function headers(array $headerValues): HtmxAttribute {
+    $this->createJsonAttribute('headers', $headerValues);
+    return $this;
+  }
+
+  /**
+   * Prevent sensitive data being saved to the history cache.
+   *
+   * Set the hx-history attribute to false on any element in the current
+   * document, or any html fragment loaded into the current document by htmx,
+   * to prevent sensitive data being saved to the localStorage cache when htmx
+   * takes a snapshot of the page state.
+   *
+   * @param bool $value
+   *   Sets the string value to 'true' or 'false'. Defaults to FALSE.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-history/
+   */
+  public function history(bool $value = FALSE): HtmxAttribute {
+    if ($value) {
+      $this->createStringAttribute('history', 'true');
+    }
+    else {
+      $this->createStringAttribute('history', 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * The element to snapshot and restore during history navigation.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-history-elt/
+   */
+  public function historyElement(): HtmxAttribute {
+    $this->createBooleanAttribute('history-elt', TRUE);
+    return $this;
+  }
+
+  /**
+   * Include additional element values in HTMX requests.
+   *
+   * The descriptor syntax is the same as hx-target. See the documentation
+   * link below for more details.
+   *
+   * @param string $descriptors
+   *   The element descriptors.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-include/
+   */
+  public function include(string $descriptors): HtmxAttribute {
+    $this->createStringAttribute('include', $descriptors);
+    return $this;
+  }
+
+  /**
+   * The element to put the htmx-request class on during the request.
+   *
+   * @param string $selector
+   *   The element CSS selector value. Selector may be prefixed with `closest`.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-indicator/
+   */
+  public function indicator(string $selector): HtmxAttribute {
+    $this->createStringAttribute('indicator', $selector);
+    return $this;
+  }
+
+  /**
+   * Control automatic attribute inheritance for child nodes.
+   *
+   * HTMX evaluates attribute inheritance with hx-inherit in two ways when
+   * hx-inherit is set on a parent node:
+   *  - data-hx-inherit="*"
+   *    All attribute inheritance for this element will be enabled.
+   * - data-hx-hx-inherit="hx-select hx-get hx-target"
+   *   Enable inheritance for only one or multiple specified attributes.
+   *
+   * @param string $attributes
+   *   The attributes to inherit.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-inherit/
+   */
+  public function inherit(string $attributes): HtmxAttribute {
+    $this->createStringAttribute('inherit', $attributes);
+    return $this;
+  }
+
+  /**
+   * Filters the parameters that will be submitted with a request.
+   *
+   * @param string $filter
+   *   The filter string. Multiple syntax options, see the link below.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-params/
+   */
+  public function params(string $filter): HtmxAttribute {
+    $this->createStringAttribute('params', $filter);
+    return $this;
+  }
+
+  /**
+   * Specifies elements to keep unchanged between requests.
+   *
+   * @param string $id
+   *   The id attribute of the element to preserve.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-preserve/
+   */
+  public function preserve(string $id): HtmxAttribute {
+    $this->createStringAttribute('preserve', $id);
+    return $this;
+  }
+
+  /**
+   * Shows a prompt() before submitting a request.
+   *
+   * @param string $message
+   *   The message to display in the prompt.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-prompt/
+   */
+  public function prompt(string $message): HtmxAttribute {
+    $this->createStringAttribute('prompt', $message);
+    return $this;
+  }
+
+  /**
+   * Control URLs in the browser location bar.
+   *
+   * Use a boolean when this attribute is added along with a request:
+   * - true: replaces the fetched URL in the browser navigation bar.
+   * - false: disables replacing the fetched URL if it would otherwise be
+   *   replaced due to inheritance.
+   *
+   * Use a URL to replace the value in the location bar. This may be relative or
+   * absolute, as per history.replaceState().
+   *
+   * @param bool|\Drupal\Core\Url $value
+   *   Use a Url object or a boolean, depending on use case.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-replace-url/
+   */
+  public function replaceUrl(bool|Url $value): HtmxAttribute {
+    if ($value instanceof Url) {
+      $this->createStringAttribute('replace-url', $value->toString());
+    }
+    else {
+      $this->createStringAttribute('replace-url', $value ? 'true' : 'false');
+    }
+    return $this;
+  }
+
+  /**
+   * Configures various aspects of the request.
+   *
+   * The hx-request attribute supports the following configuration values:
+   * - timeout: (integer) the timeout for the request, in milliseconds.
+   * - credentials: (boolean) if the request will send credentials.
+   * - noHeaders: (boolean) strips all headers from the request.
+   *
+   * Dynamic javascript values are not supported for security and for
+   * simplicity.  If you need calculated values you should do determine them
+   * here on the server-side
+   *
+   * @param array<string, int|bool> $configValues
+   *   The configuration values as name => value.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-headers/
+   */
+  public function request(array $configValues): HtmxAttribute {
+    $this->createJsonAttribute('request', $configValues);
+    return $this;
+  }
+
+  /**
+   * Synchronize AJAX requests between multiple elements.
+   *
+   * @param string $selector
+   *   A CSS selector followed by a strategy.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-sync/
+   */
+  public function sync(string $selector): HtmxAttribute {
+    $this->createStringAttribute('sync', $selector);
+    return $this;
+  }
+
+  /**
+   * Cause an element to validate itself before it submits a request.
+   *
+   * @param bool $value
+   *   Should the element validate before the request.
+   *
+   * @return $this
+   *
+   * @see https://htmx.org/attributes/hx-validate/
+   */
+  public function validate(bool $value = TRUE): HtmxAttribute {
+    if ($value) {
+      $this->createStringAttribute('validate', 'true');
+    }
+    else {
+      $this->createStringAttribute('validate', 'false');
+    }
+    return $this;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 5afa135d02682b552c2c7df9cb4a223ba085edcf..ea6a10db144571818649bbe637e2adcf750a056c 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -254,7 +254,7 @@ public function getUrl($name, $parameters = [], $options = []) {
    *   The link text for the anchor tag as a translated string.
    * @param \Drupal\Core\Url|string $url
    *   The URL object or string used for the link.
-   * @param array|\Drupal\Core\Template\Attribute $attributes
+   * @param array|HtmlAttributeInterface $attributes
    *   An optional array or Attribute object of link attributes.
    *
    * @return array
@@ -262,7 +262,7 @@ public function getUrl($name, $parameters = [], $options = []) {
    */
   public function getLink($text, $url, $attributes = []) {
     assert(is_string($url) || $url instanceof Url, '$url must be a string or object of type \Drupal\Core\Url');
-    assert(is_array($attributes) || $attributes instanceof Attribute, '$attributes, if set, must be an array or object of type \Drupal\Core\Template\Attribute');
+    assert(is_array($attributes) || $attributes instanceof HtmlAttributeInterface, '$attributes, if set, must be an array or object implementing HtmlAttributeInterface');
 
     if (!$url instanceof Url) {
       $url = Url::fromUri($url);
@@ -272,7 +272,7 @@ public function getLink($text, $url, $attributes = []) {
     // @see https://www.drupal.org/node/2842399
     $url = clone $url;
     if ($attributes) {
-      if ($attributes instanceof Attribute) {
+      if ($attributes instanceof HtmlAttributeInterface) {
         $attributes = $attributes->toArray();
       }
       $url->mergeOptions(['attributes' => $attributes]);
@@ -621,14 +621,14 @@ public function safeJoin(Environment $env, $value, $glue = '') {
   /**
    * Creates an Attribute object.
    *
-   * @param Attribute|array $attributes
+   * @param \Drupal\Core\Template\HtmlAttributeInterface|array $attributes
    *   (optional) An existing attribute object or an associative array of
    *   key-value pairs to be converted to HTML attributes.
    *
-   * @return \Drupal\Core\Template\Attribute
+   * @return \Drupal\Core\Template\HtmlAttributeInterface
    *   An attributes object that has the given attributes.
    */
-  public function createAttribute(Attribute|array $attributes = []) {
+  public function createAttribute(HtmlAttributeInterface|array $attributes = []) {
     if (\is_array($attributes)) {
       return new Attribute($attributes);
     }
diff --git a/core/lib/Drupal/Core/Theme/ThemeManager.php b/core/lib/Drupal/Core/Theme/ThemeManager.php
index 8962896ee3ef21d3e9bd8ce7717630e2700cb4a5..470b3fa8f79b55e49dcfa609d210aa2a9643d4bf 100644
--- a/core/lib/Drupal/Core/Theme/ThemeManager.php
+++ b/core/lib/Drupal/Core/Theme/ThemeManager.php
@@ -7,6 +7,7 @@
 use Drupal\Core\Routing\StackedRouteMatchInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\HtmlAttributeInterface;
 use Drupal\Core\Template\AttributeHelper;
 use Drupal\Core\Utility\CallableResolver;
 
@@ -340,7 +341,7 @@ public function render($hook, array $variables) {
       $default_attributes = new Attribute();
     }
     foreach (['attributes', 'title_attributes', 'content_attributes'] as $key) {
-      if (isset($variables[$key]) && !($variables[$key] instanceof Attribute)) {
+      if (isset($variables[$key]) && !($variables[$key] instanceof HtmlAttributeInterface)) {
         if ($variables[$key]) {
           $variables[$key] = new Attribute($variables[$key]);
         }
diff --git a/core/misc/cspell/dictionary.txt b/core/misc/cspell/dictionary.txt
index 83fe358eb459b73b03a8f604ee3b36a661326d0f..c0f4912e057db3cf5fda073ddabb676bcf51f69b 100644
--- a/core/misc/cspell/dictionary.txt
+++ b/core/misc/cspell/dictionary.txt
@@ -222,6 +222,7 @@ hmac
 hookname
 hrefs
 htmlcorrector
+htmx
 httpheader
 httponly
 icann
@@ -418,6 +419,8 @@ restrictor
 restripe
 restriped
 restui
+reswap
+retarget
 revisionable
 revisioned
 revisionid
diff --git a/core/misc/htmx-behaviors.js b/core/misc/htmx-behaviors.js
new file mode 100644
index 0000000000000000000000000000000000000000..add7b9502d491fb6947590871776d68c4b54c904
--- /dev/null
+++ b/core/misc/htmx-behaviors.js
@@ -0,0 +1,227 @@
+/**
+ * @file
+ * Connect Drupal javascript to htmx inserted content.
+ */
+
+// Drupal core standard practice: wrap JS in an anonymous closure.
+(function (Drupal, drupalSettings, once, htmx, loadjs) {
+  // Enforce the declared dependency on HTMX.
+  if (typeof htmx !== 'object' || !htmx.hasOwnProperty('process')) {
+    return;
+  }
+
+  /**
+   * Attaches Drupal behaviors to markup inserted by HTMX.
+   *
+   * @param {Event} htmxLoadEvent
+   *   Event returned from HTMX loading processes.
+   */
+  function htmxDrupalBehaviors(htmxLoadEvent) {
+    // The attachBehaviors method searches within the context.
+    // We need to go up one level so that the loaded content is processed
+    // completely.
+    Drupal.attachBehaviors(
+      htmxLoadEvent.detail.elt?.parentElement,
+      drupalSettings,
+    );
+  }
+
+  /**
+   * Includes Drupal data with HTMX requests.
+   *
+   * @param {Event} configRequestEvent
+   *   The event passed from HTMX as it configures a request.
+   */
+  function htmxDrupalData(configRequestEvent) {
+    const url = new URL(configRequestEvent.detail.path, document.location.href);
+    const origin = document.location.origin;
+    const sameHost = origin === url.origin;
+    if (sameHost) {
+      // We only need to add this data for htmx requests back to the site.
+      configRequestEvent.detail.headers['HX-Page-State'] =
+        drupalSettings.ajaxPageState.libraries;
+      // Swap in drupal data selectors as #id values are altered to be unique.
+      configRequestEvent.detail.headers['HX-Target'] =
+        configRequestEvent.detail.target.dataset.drupalSelector;
+      configRequestEvent.detail.headers['HX-Trigger'] =
+        configRequestEvent.detail.elt.dataset.drupalSelector;
+    }
+  }
+
+  /**
+   * Processes asset information from the response to an HTMX request.
+   *
+   * @param {Event} oobSwapEvent
+   *   The htmx:oobAfterSwap event triggered by HTMX.
+   */
+  function htmxDrupalAssetProcessor(oobSwapEvent) {
+    /**
+     * Local helper function to merge two objects recursively.
+     *
+     * @param current
+     *   The object to receive the merged values.
+     * @param sources
+     *   The objects to merge into current.
+     *
+     * @see https://youmightnotneedjquery.com/#deep_extend
+     */
+    function mergeSettings(current, ...sources) {
+      if (!current) {
+        return {};
+      }
+
+      sources
+        .filter((obj) => Boolean(obj))
+        .forEach((obj) => {
+          Object.entries(obj).forEach(([key, value]) => {
+            switch (Object.prototype.toString.call(value)) {
+              case '[object Object]':
+                current[key] = current[key] || {};
+                current[key] = mergeSettings(current[key], value);
+                break;
+
+              case '[object Array]':
+                current[key] = mergeSettings(new Array(value.length), value);
+                break;
+
+              default:
+                current[key] = value;
+            }
+          });
+        });
+
+      return current;
+    }
+
+    // Find any inserted assets.
+    const assetsTag = oobSwapEvent.detail.target.querySelector(
+      'script[data-drupal-selector="drupal-htmx-assets"]',
+    );
+    if (!(assetsTag instanceof HTMLElement)) {
+      return;
+    }
+    // Parse assets and initialize container variables.
+    const assets = JSON.parse(assetsTag.textContent);
+    let cssItems = [];
+    let scriptItems = [];
+    let scriptBottomItems = [];
+    let paths = [];
+    if (assets.constructor.name === 'Object') {
+      // Variable assets should have properties 'styles', 'scripts,
+      // 'scripts_bottom', 'settings'. See
+      // HtmxResponseAttachmentsProcessor::processAssetLibraries
+      cssItems = new Map(
+        assets.styles.map((item) => [`css!${item['#attributes'].href}`, item]),
+      );
+      scriptItems = new Map(
+        assets.scripts.map((item) => [item['#attributes'].src, item]),
+      );
+      scriptBottomItems = new Map(
+        assets.scripts_bottom.map((item) => [item['#attributes'].src, item]),
+      );
+      mergeSettings(drupalSettings, assets.settings);
+    }
+    // Load CSS.
+    if (cssItems instanceof Map && cssItems.size > 0) {
+      // Fetch in parallel but load in sequence.
+      cssItems.forEach((value, key) => paths.push(key));
+      loadjs(paths, {
+        async: false,
+        before(path, linkElement) {
+          const item = cssItems.get(path);
+          Object.entries(item['#attributes']).forEach(
+            ([attributeKey, attributeValue]) => {
+              linkElement.setAttribute(attributeKey, attributeValue);
+            },
+          );
+        },
+      });
+    }
+    /* By default, loadjs appends the script to the head. When scripts
+     * are loaded via HTMX, their location has no impact on
+     * functionality. But, since Drupal loaded scripts can choose
+     * their parent element, we provide that option here for the sake of
+     * consistency.
+     */
+    if (scriptItems instanceof Map && scriptItems.size > 0) {
+      paths = [];
+      scriptItems.forEach((value, key) => paths.push(key));
+      // Load head JS.
+      // Fetch in parallel but load in sequence.
+      loadjs(paths, {
+        async: false,
+        before(path, scriptElement) {
+          const item = scriptItems.get(path);
+          Object.entries(item['#attributes']).forEach(
+            ([attributeKey, attributeValue]) => {
+              scriptElement.setAttribute(attributeKey, attributeValue);
+            },
+          );
+        },
+      });
+    }
+    if (scriptBottomItems instanceof Map && scriptBottomItems.size > 0) {
+      paths = [];
+      scriptBottomItems.forEach((value, key) => paths.push(key));
+      // Fetch in parallel but load in sequence.
+      loadjs(paths, {
+        async: false,
+        before(path, scriptElement) {
+          const item = scriptBottomItems.get(path);
+          Object.entries(item['#attributes']).forEach(
+            ([attributeKey, attributeValue]) => {
+              scriptElement.setAttribute(attributeKey, attributeValue);
+            },
+          );
+          document.body.appendChild(scriptElement);
+          // Return false to bypass loadjs' default DOM insertion
+          // mechanism.
+          return false;
+        },
+      });
+    }
+    // Any assets now processed.  Remove the found asset tag.
+    htmx.remove(assetsTag);
+  }
+
+  /* Initialize listeners. */
+
+  /**
+   * Process new content through HTMX.
+   *
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Process all new content in case any HTMX attributes are in that content.
+   */
+  Drupal.behaviors.htmxProcess = {
+    attach(context) {
+      htmx.process(context);
+    },
+  };
+
+  /**
+   * Set listeners for the HTMX events that power our integration.
+   *
+   * @type {{attach: Drupal.behaviors.htmxBehaviors.attach}}
+   */
+  Drupal.behaviors.htmxBehaviors = {
+    attach: () => {
+      // JS should use native methods to enforce a single instance of our event
+      // handlers since we used named functions.  Use the `once` library to be
+      // consistent with the rest of core.
+      if (!once('htmxBehaviors', 'html').length) {
+        return;
+      }
+      // Fired by HTMX before a request is sent.
+      window.addEventListener('htmx:configRequest', htmxDrupalData);
+      // Fired by HTMX after an 'out of band' content swap, which we use to add
+      // asset info from the response.
+      window.addEventListener('htmx:oobAfterSwap', htmxDrupalAssetProcessor);
+      // Attach Drupal behaviors after a normal HTMX content swap.
+      window.addEventListener('htmx:load', htmxDrupalBehaviors);
+      // Attach Drupal behaviors after an HTMX 'out of band' content swap.
+      window.addEventListener('htmx:oobAfterSwap', htmxDrupalBehaviors);
+    },
+  };
+})(Drupal, drupalSettings, once, htmx, loadjs);
diff --git a/core/modules/config/src/Form/ConfigSingleExportForm.php b/core/modules/config/src/Form/ConfigSingleExportForm.php
index 963a6a1d9d41080246498c71c4e3557dcbe417ea..7b27b91d74b8d2816723ef1c31db067c7ca3c2e7 100644
--- a/core/modules/config/src/Form/ConfigSingleExportForm.php
+++ b/core/modules/config/src/Form/ConfigSingleExportForm.php
@@ -2,15 +2,20 @@
 
 namespace Drupal\config\Form;
 
+use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
 use Drupal\Core\Config\StorageInterface;
-use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Form\FormBase;
-use Drupal\Core\Form\FormState;
 use Drupal\Core\Form\FormStateInterface;
-use Drupal\Core\Serialization\Yaml;
+use Drupal\Core\Http\HttpMethod;
+use Drupal\Core\Render\Hypermedia\Htmx;
+use Drupal\Core\Render\Hypermedia\Operations\Replace;
 use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\HtmxAttribute;
+use Drupal\Core\Url;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
@@ -74,7 +79,13 @@ public function getFormId() {
   /**
    * {@inheritdoc}
    */
-  public function buildForm(array $form, FormStateInterface $form_state, $config_type = NULL, $config_name = NULL) {
+  public function buildForm(array $form, FormStateInterface $form_state, ?string $config_type = NULL, ?string $config_name = NULL) {
+    // Default types allow us to extend the form signature but Drupal actually
+    // passes NULL if the parameters are not in the route.  Insure we have a
+    // string.
+    $config_type = $config_type ?? '';
+    $config_name = $config_name ?? '';
+    $trigger = $this->getHtmxTrigger();
     $form['#prefix'] = '<div id="js-config-form-wrapper">';
     $form['#suffix'] = '</div>';
     foreach ($this->entityTypeManager->getDefinitions() as $entity_type => $definition) {
@@ -82,6 +93,7 @@ public function buildForm(array $form, FormStateInterface $form_state, $config_t
         $this->definitions[$entity_type] = $definition;
       }
     }
+
     $entity_types = array_map(function (EntityTypeInterface $definition) {
       return $definition->getLabel();
     }, $this->definitions);
@@ -90,28 +102,49 @@ public function buildForm(array $form, FormStateInterface $form_state, $config_t
     $config_types = [
       'system.simple' => $this->t('Simple configuration'),
     ] + $entity_types;
+
+    // Prepare an Htmx object for each dynamic select.
+    $config_type_htmx = new Htmx();
+    $config_name_htmx = new Htmx();
+
+    /*
+     * - Send a POST request to the form URL.
+     * - Select the config_name <select> element from the response.
+     * - Target the config_name <select> in the rendered form for replacement.
+     * - Replace uses the outerHTML strategy, which is to replace the whole tag.
+     */
+    $form_url = Url::fromRoute(
+      route_name: 'config.export_single',
+      route_parameters: ['config_type' => $config_type, 'config_name' => $config_name],
+    );
+    $config_type_htmx->setRequestOperation(
+      (new Replace())
+        ->setRequest(HttpMethod::Post, $form_url)
+        ->select('select[data-drupal-selector="edit-config-name"]')
+        ->target('select[data-drupal-selector="edit-config-name"]')
+    );
     $form['config_type'] = [
       '#title' => $this->t('Configuration type'),
       '#type' => 'select',
       '#options' => $config_types,
       '#default_value' => $config_type,
-      '#ajax' => [
-        'callback' => '::updateConfigurationType',
-        'wrapper' => 'js-config-form-wrapper',
-      ],
+      '#htmx' => $config_type_htmx,
     ];
+
     $default_type = $form_state->getValue('config_type', $config_type);
+    $config_name_htmx->setRequestOperation(
+      (new Replace())
+        ->setRequest(HttpMethod::Post, $form_url)
+        ->select('#edit-export-wrapper')
+        ->target('#edit-export-wrapper')
+    );
     $form['config_name'] = [
       '#title' => $this->t('Configuration name'),
       '#type' => 'select',
-      '#options' => $this->findConfiguration($default_type),
+      '#options' => $this->findConfiguration($default_type, $form_state),
+      '#empty_value' => '',
       '#default_value' => $config_name,
-      '#prefix' => '<div id="edit-config-type-wrapper">',
-      '#suffix' => '</div>',
-      '#ajax' => [
-        'callback' => '::updateExport',
-        'wrapper' => 'edit-export-wrapper',
-      ],
+      '#htmx' => $config_name_htmx,
     ];
 
     $form['export'] = [
@@ -121,54 +154,82 @@ public function buildForm(array $form, FormStateInterface $form_state, $config_t
       '#prefix' => '<div id="edit-export-wrapper">',
       '#suffix' => '</div>',
     ];
-    if ($config_type && $config_name) {
-      $fake_form_state = (new FormState())->setValues([
-        'config_type' => $config_type,
-        'config_name' => $config_name,
-      ]);
-      $form['export'] = $this->updateExport($form, $fake_form_state);
+    if ($trigger === 'edit-config-type') {
+      // Type has changed.
+      $form['export']['#value'] = NULL;
+      // Also replace the wrapped export element when the response is returned.
+      // See https://htmx.org/attributes/hx-swap-oob/ for a detailed description
+      // of selection and targeting with ::swapOob.
+      // Since this is placed directly in the prefix string, use an
+      // HtmxAttribute object directly and merge it with standard attributes.
+      $attributes = new Attribute(['id' => 'edit-export-wrapper']);
+      $export_htmx_attributes = new HtmxAttribute();
+      $export_htmx_attributes->swapOob('outerHTML:#edit-export-wrapper');
+      $attributes = $attributes->merge($export_htmx_attributes);
+      $form['export']['#prefix'] = '<div  ' . $attributes . '>';
+    }
+    elseif ($trigger === 'edit-config-name') {
+      // A name is selected.
+      $default_name = $form_state->getValue('config_name', $config_name);
+      $form['export'] = $this->updateExport($form['export'], $default_type, $default_name);
+      // Also update the browser URL.
+      $push = Url::fromRoute(
+        route_name: 'config.export_single',
+        route_parameters: ['config_type' => $default_type, 'config_name' => $default_name],
+      );
+      $config_name_htmx->headers->pushUrl($push);
+    }
+    elseif ($config_type && $config_name) {
+      $form['export'] = $this->updateExport($form['export'], $config_type, $config_name);
     }
-    return $form;
-  }
-
-  /**
-   * Handles switching the configuration type selector.
-   */
-  public function updateConfigurationType($form, FormStateInterface $form_state) {
-    $form['config_name']['#options'] = $this->findConfiguration($form_state->getValue('config_type'));
-    $form['export']['#value'] = NULL;
     return $form;
   }
 
   /**
    * Handles switching the export textarea.
+   *
+   * @param array $element
+   *   The export element render array.
+   * @param string $config_type
+   *   The config type ID.
+   * @param string $config_name
+   *   The config name ID.
+   *
+   * @return array
+   *   The modified export element render array.
    */
-  public function updateExport($form, FormStateInterface $form_state) {
+  public function updateExport(array $element, string $config_type, string $config_name) {
     // Determine the full config name for the selected config entity.
-    if ($form_state->getValue('config_type') !== 'system.simple') {
-      $definition = $this->entityTypeManager->getDefinition($form_state->getValue('config_type'));
-      $name = $definition->getConfigPrefix() . '.' . $form_state->getValue('config_name');
+    if (!empty($config_type) && $config_type !== 'system.simple' && !empty($config_name)) {
+      $definition = $this->entityTypeManager->getDefinition($config_type);
+      $name = $definition->getConfigPrefix() . '.' . $config_name;
     }
     // The config name is used directly for simple configuration.
     else {
-      $name = $form_state->getValue('config_name');
+      $name = $config_name;
     }
     // Read the raw data for this config name, encode it, and display it.
     $exists = $this->configStorage->exists($name);
-    $form['export']['#value'] = !$exists ? NULL : Yaml::encode($this->configStorage->read($name));
-    $form['export']['#description'] = !$exists ? NULL : $this->t('Filename: %name', ['%name' => $name . '.yml']);
-    return $form['export'];
+    $element['#value'] = !$exists ? NULL : Yaml::encode($this->configStorage->read($name));
+    $element['#description'] = !$exists ? NULL : $this->t('Filename: %name', ['%name' => $name . '.yml']);
+    return $element;
   }
 
   /**
    * Handles switching the configuration type selector.
+   *
+   * @param string $config_type
+   *   The selected configuration type.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current form state.
+   *
+   * @return array
+   *   An array of matching items.
    */
-  protected function findConfiguration($config_type) {
-    $names = [
-      '' => $this->t('- Select -'),
-    ];
+  protected function findConfiguration($config_type, FormStateInterface $form_state) {
+    $names = [];
     // For a given entity type, load all entities.
-    if ($config_type && $config_type !== 'system.simple') {
+    if ($config_type !== 'system.simple' && !empty($config_type)) {
       $entity_storage = $this->entityTypeManager->getStorage($config_type);
       foreach ($entity_storage->loadMultiple() as $entity) {
         $entity_id = $entity->id();
diff --git a/core/modules/file/src/Plugin/Field/FieldFormatter/FileMediaFormatterBase.php b/core/modules/file/src/Plugin/Field/FieldFormatter/FileMediaFormatterBase.php
index c00f4aeb397b7f333eb8af594dae94fbf8f1f8c7..08af0c0793b7ab3b7a36702010bd69d8b3528d24 100644
--- a/core/modules/file/src/Plugin/Field/FieldFormatter/FileMediaFormatterBase.php
+++ b/core/modules/file/src/Plugin/Field/FieldFormatter/FileMediaFormatterBase.php
@@ -146,7 +146,7 @@ public function viewElements(FieldItemListInterface $items, $langcode) {
    *   Additional attributes to be applied to the HTML element. Attribute names
    *   will be used as key and value in the HTML element.
    *
-   * @return \Drupal\Core\Template\Attribute
+   * @return \Drupal\Core\Template\HtmlAttributeInterface
    *   Container with all the attributes for the HTML tag.
    */
   protected function prepareAttributes(array $additional_attributes = []) {
diff --git a/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.info.yml b/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.info.yml
new file mode 100644
index 0000000000000000000000000000000000000000..82db4315f10bc5851fec6d642a4091552db5e2a9
--- /dev/null
+++ b/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.info.yml
@@ -0,0 +1,5 @@
+name: 'HTMX Header test'
+type: module
+description: 'Provides routes that return render arrays for testing HtmxResponseHeader methods.'
+package: Testing
+version: VERSION
diff --git a/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.routing.yml b/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.routing.yml
new file mode 100644
index 0000000000000000000000000000000000000000..3afb9d8c5272efb8a825ff47b88663115e371ecf
--- /dev/null
+++ b/core/modules/system/tests/modules/htmx_headers_test/htmx_headers_test.routing.yml
@@ -0,0 +1,103 @@
+htmx_headers_test.location_url:
+  path: '/test-htmx-headers/location-url'
+  defaults:
+    _title: 'Location: URL'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::locationUrl'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.location_json:
+  path: '/test-htmx-headers/location-json'
+  defaults:
+    _title: 'Location: JSON'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::locationJson'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.push_url:
+  path: '/test-htmx-headers/push-url'
+  defaults:
+    _title: 'Push-url'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::pushUrl'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.push_url_false:
+  path: '/test-htmx-headers/push-url-false'
+  defaults:
+    _title: 'Push-url false'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::pushUrlFalse'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.replace_url:
+  path: '/test-htmx-headers/replace-url'
+  defaults:
+    _title: 'Replace-url'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::replaceUrl'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.replace_url_false:
+  path: '/test-htmx-headers/replace-url-false'
+  defaults:
+    _title: 'Replace-url false'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::replaceUrlFalse'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.refresh:
+  path: '/test-htmx-headers/refresh'
+  defaults:
+    _title: 'Refresh'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::refresh'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.reselect:
+  path: '/test-htmx-headers/reselect'
+  defaults:
+    _title: 'Reselect'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::reselect'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.redirect:
+  path: '/test-htmx-headers/redirect'
+  defaults:
+    _title: 'Redirect'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::redirectHeader'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.reswap:
+  path: '/test-htmx-headers/reswap'
+  defaults:
+    _title: 'Reswap'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::reswap'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.retarget:
+  path: '/test-htmx-headers/retarget'
+  defaults:
+    _title: 'Retarget'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::retarget'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.triggers:
+  path: '/test-htmx-headers/triggers'
+  defaults:
+    _title: 'Triggers'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::triggers'
+  requirements:
+    _permission: 'access content'
+
+htmx_headers_test.triggers_json:
+  path: '/test-htmx-headers/triggers-json'
+  defaults:
+    _title: 'Triggers'
+    _controller: '\Drupal\htmx_headers_test\Controller\TestHtmxHeadersController::triggersJson'
+  requirements:
+    _permission: 'access content'
diff --git a/core/modules/system/tests/modules/htmx_headers_test/src/Controller/TestHtmxHeadersController.php b/core/modules/system/tests/modules/htmx_headers_test/src/Controller/TestHtmxHeadersController.php
new file mode 100644
index 0000000000000000000000000000000000000000..1180aaed50f5211c79987e7b1a8ca56b034bf662
--- /dev/null
+++ b/core/modules/system/tests/modules/htmx_headers_test/src/Controller/TestHtmxHeadersController.php
@@ -0,0 +1,308 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\htmx_headers_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Url;
+use Drupal\Core\Http\HtmxLocationResponseData;
+use Drupal\Core\Http\HtmxResponseHeaders;
+
+/**
+ * Returns responses for HTMX Header test routes.
+ */
+final class TestHtmxHeadersController extends ControllerBase {
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function locationUrl(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->location($this->getUrl());
+    $build['content'] = [
+      '#markup' => $this->t('Location'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Helper function to build a sample url.
+   *
+   * @return \Drupal\Core\Url
+   *   The url object.
+   */
+  protected function getUrl(): Url {
+    return Url::fromRoute('<front>');
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function locationJson(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $data = new HtmxLocationResponseData(
+      path: $this->getUrl(),
+      source: 'source-value',
+      event: 'event-value',
+      headers: ['Header-one' => 'one'],
+      handler: 'handler-value',
+      target: 'target-value',
+      swap: 'swap-value',
+      select: 'select-value',
+      values: ['one' => '1', 'two' => '2'],
+    );
+    $htmxHeaders->location($data);
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('Location'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function pushUrlFalse(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->pushUrl(FALSE);
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('pushUrl'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function pushUrl(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->pushUrl($this->getUrl());
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('pushUrl'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function replaceUrlFalse(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->replaceUrl(FALSE);
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('pushUrl'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function replaceUrl(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->replaceUrl($this->getUrl());
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('replaceUrl'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function redirectHeader(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->redirect($this->getUrl());
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('redirect'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function refresh(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->refresh(TRUE);
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('refresh'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function reswap(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->reswap('swap-value');
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('reswap'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function retarget(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->retarget('retarget-value');
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('retarget'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function reselect(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->reselect('reselect-value');
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('reselect'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function triggers(): array {
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->trigger('trigger-value')
+      ->triggerAfterSettle('trigger-value')
+      ->triggerAfterSwap('trigger-value');
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('reselect'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+  /**
+   * Builds the response with header.
+   *
+   * @return array
+   *   The render array
+   */
+  public function triggersJson(): array {
+    $data = [
+      'showMessage' =>
+        [
+          'level' => 'info',
+          'message' => 'Here Is A Message',
+        ],
+    ];
+    $htmxHeaders = new HtmxResponseHeaders();
+    $htmxHeaders->trigger($data)
+      ->triggerAfterSettle($data)
+      ->triggerAfterSwap($data);
+    $build['content'] = [
+      '#type' => 'item',
+      '#markup' => $this->t('reselect'),
+      '#attached' => [
+        'http_header' => $htmxHeaders->toArray(),
+      ],
+    ];
+
+    return $build;
+  }
+
+}
diff --git a/core/modules/views/views.theme.inc b/core/modules/views/views.theme.inc
index 10c29c5dbf30aef72682d9dbda9409f8cc3360f2..386ae320c41c192b2a36e27b4175b170de5de755 100644
--- a/core/modules/views/views.theme.inc
+++ b/core/modules/views/views.theme.inc
@@ -7,6 +7,7 @@
 use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\Xss;
 use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\HtmlAttributeInterface;
 use Drupal\Core\Url;
 use Drupal\Core\Utility\TableSort;
 
@@ -557,7 +558,7 @@ function template_preprocess_views_view_table(&$variables): void {
       if (!isset($column_reference['attributes'])) {
         $column_reference['attributes'] = new Attribute();
       }
-      elseif (!($column_reference['attributes'] instanceof Attribute)) {
+      elseif (!($column_reference['attributes'] instanceof HtmlAttributeInterface)) {
         $column_reference['attributes'] = new Attribute($column_reference['attributes']);
       }
 
diff --git a/core/scripts/js/vendor-update.js b/core/scripts/js/vendor-update.js
index db7e8a36670b48fde9cbb70da0c50d33a837eb01..68183a2aabde35ed3ab92b0d74f2e8e3afc96746 100644
--- a/core/scripts/js/vendor-update.js
+++ b/core/scripts/js/vendor-update.js
@@ -79,6 +79,15 @@ const assetsFolder = `${coreFolder}/assets/vendor`;
       library: 'internal.backbone',
       files: ['backbone.js', 'backbone-min.js', 'backbone-min.js.map'],
     },
+    {
+      pack: 'htmx.org',
+      folder: 'htmx',
+      library: 'htmx',
+      files: [
+        { from: 'dist/htmx.min.js', to: 'htmx.min.js' },
+        { from: 'dist/ext/debug.js', to: 'debug.js' },
+      ],
+    },
     {
       pack: 'jquery',
       files: [
diff --git a/core/tests/Drupal/KernelTests/Core/Http/HtmxHeaderTest.php b/core/tests/Drupal/KernelTests/Core/Http/HtmxHeaderTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..ef3fc944365a461dbc88787506039956c108b30f
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Http/HtmxHeaderTest.php
@@ -0,0 +1,126 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\KernelTests\Core\Http;
+
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Test the header builder.
+ *
+ * @group Http
+ *
+ * @coversDefaultClass \Drupal\Core\Http\HtmxResponseHeaders
+ */
+final class HtmxHeaderTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['system', 'user', 'htmx_headers_test'];
+
+  /**
+   * Injected entity type manager.
+   */
+  protected EntityTypeManagerInterface $entityTypeManager;
+
+  /**
+   * Set up the test.
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->entityTypeManager = $this->container->get('entity_type.manager');
+    $this->installEntitySchema('user_role');
+    $this->installEntitySchema('user');
+    $this->installConfig(['user']);
+    $this->container
+      ->get('module_handler')
+      ->loadInclude('user', 'install');
+    user_install();
+    /** @var \Drupal\user\Entity\Role $anonymous */
+    $anonymous = $this->entityTypeManager->getStorage('user_role')->load('anonymous');
+    $anonymous->grantPermission('access content')->save();
+  }
+
+  /**
+   * Test all the headers.
+   *
+   * @covers ::location
+   * @covers ::pushUrl
+   * @covers ::replaceUrl
+   * @covers ::refresh
+   * @covers ::reswap
+   * @dataProvider hxHeaderDataProvider
+   */
+  public function testHeaders(string $path, string $headerName, string $headerValue): void {
+    $httpKernel = $this->container->get('http_kernel');
+    $request = Request::create($path);
+    $response = $httpKernel->handle($request);
+    $this->assertTrue($response->headers->has($headerName));
+    $value = $response->headers->get($headerName);
+    $this->assertEquals($headerValue, $value);
+  }
+
+  /**
+   * Data provider for ::testHeaders.
+   */
+  public static function hxHeaderDataProvider(): array {
+    return [
+      ['/test-htmx-headers/location-url', 'HX-Location', '/'],
+      [
+        '/test-htmx-headers/location-json',
+        'HX-Location',
+        '{"path":"\/","source":"source-value","event":"event-value","headers":{"Header-one":"one"},"handler":"handler-value","target":"target-value","swap":"swap-value","select":"select-value","values":{"one":"1","two":"2"}}',
+      ],
+      ['/test-htmx-headers/push-url', 'HX-Push-Url', '/'],
+      ['/test-htmx-headers/push-url-false', 'HX-Push-Url', 'false'],
+      ['/test-htmx-headers/replace-url', 'HX-Replace-Url', '/'],
+      ['/test-htmx-headers/replace-url-false', 'HX-Replace-Url', 'false'],
+      ['/test-htmx-headers/redirect', 'HX-Redirect', '/'],
+      ['/test-htmx-headers/refresh', 'HX-Refresh', 'true'],
+      ['/test-htmx-headers/reswap', 'HX-Reswap', 'swap-value'],
+      ['/test-htmx-headers/retarget', 'HX-Retarget', 'retarget-value'],
+      ['/test-htmx-headers/reselect', 'HX-Reselect', 'reselect-value'],
+    ];
+  }
+
+  /**
+   * Test trigger headers with just an event name.
+   */
+  public function testSimpleTriggers(): void {
+    $httpKernel = $this->container->get('http_kernel');
+    $request = Request::create('/test-htmx-headers/triggers');
+    $response = $httpKernel->handle($request);
+    $this->assertTrue($response->headers->has('HX-Trigger'));
+    $this->assertTrue($response->headers->has('HX-Trigger-After-Settle'));
+    $this->assertTrue($response->headers->has('HX-Trigger-After-Swap'));
+    $value = $response->headers->get('HX-Trigger');
+    $this->assertEquals('trigger-value', $value);
+    $value = $response->headers->get('HX-Trigger-After-Settle');
+    $this->assertEquals('trigger-value', $value);
+    $value = $response->headers->get('HX-Trigger-After-Swap');
+    $this->assertEquals('trigger-value', $value);
+  }
+
+  /**
+   * Test triggers with JSON payload.
+   */
+  public function testJsonTriggers(): void {
+    $httpKernel = $this->container->get('http_kernel');
+    $request = Request::create('/test-htmx-headers/triggers-json');
+    $response = $httpKernel->handle($request);
+    $this->assertTrue($response->headers->has('HX-Trigger'));
+    $this->assertTrue($response->headers->has('HX-Trigger-After-Settle'));
+    $this->assertTrue($response->headers->has('HX-Trigger-After-Swap'));
+    $value = $response->headers->get('HX-Trigger');
+    $this->assertEquals('{"showMessage":{"level":"info","message":"Here Is A Message"}}', $value);
+    $value = $response->headers->get('HX-Trigger-After-Settle');
+    $this->assertEquals('{"showMessage":{"level":"info","message":"Here Is A Message"}}', $value);
+    $value = $response->headers->get('HX-Trigger-After-Swap');
+    $this->assertEquals('{"showMessage":{"level":"info","message":"Here Is A Message"}}', $value);
+  }
+
+}
diff --git a/core/tests/Drupal/KernelTests/Core/Template/HtmxAttributeTest.php b/core/tests/Drupal/KernelTests/Core/Template/HtmxAttributeTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..2536971c1f77236f619c283899baaaa759326bfd
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Template/HtmxAttributeTest.php
@@ -0,0 +1,415 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\KernelTests\Core\Template;
+
+use Drupal\Core\Url;
+use Drupal\Core\Template\HtmxAttribute;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Test description.
+ *
+ * @group htmx
+ *
+ * @coversDefaultClass \Drupal\Core\Template\HtmxAttribute
+ */
+final class HtmxAttributeTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['common_test'];
+
+  /**
+   * Class under test.
+   *
+   * @var \Drupal\Core\Template\HtmxAttribute
+   */
+  protected HtmxAttribute $htmxAttribute;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->htmxAttribute = new HtmxAttribute();
+  }
+
+  /**
+   * Test get method.
+   *
+   * @covers ::get
+   */
+  public function testHxGet(): void {
+    $url = Url::fromRoute('common_test.destination');
+    $this->htmxAttribute->get($url);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    $this->assertStringStartsWith(' data-hx-get="', $rendered);
+    $this->assertStringEndsWith('/common-test/destination"', $rendered);
+  }
+
+  /**
+   * Test get method.
+   *
+   * @covers ::post
+   */
+  public function testHxPost(): void {
+    $url = Url::fromRoute('common_test.destination');
+    $this->htmxAttribute->post($url);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    $this->assertStringStartsWith(' data-hx-post="', $rendered);
+    $this->assertStringEndsWith('/common-test/destination"', $rendered);
+  }
+
+  /**
+   * Test get method.
+   *
+   * @covers ::put
+   */
+  public function testHxPut(): void {
+    $url = Url::fromRoute('common_test.destination');
+    $this->htmxAttribute->put($url);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    $this->assertStringStartsWith(' data-hx-put="', $rendered);
+    $this->assertStringEndsWith('/common-test/destination"', $rendered);
+  }
+
+  /**
+   * Test get method.
+   *
+   * @covers ::patch
+   */
+  public function testHxPatch(): void {
+    $url = Url::fromRoute('common_test.destination');
+    $this->htmxAttribute->patch($url);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    $this->assertStringStartsWith(' data-hx-patch="', $rendered);
+    $this->assertStringEndsWith('/common-test/destination"', $rendered);
+  }
+
+  /**
+   * Test get method.
+   *
+   * @covers ::delete
+   */
+  public function testHxDelete(): void {
+    $url = Url::fromRoute('common_test.destination');
+    $this->htmxAttribute->delete($url);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    $this->assertStringStartsWith(' data-hx-delete="', $rendered);
+    $this->assertStringEndsWith('/common-test/destination"', $rendered);
+  }
+
+  /**
+   * Test on method.
+   *
+   * @covers ::on
+   * @dataProvider hxOnDataProvider
+   */
+  public function testHxOn(string $event, string $expected): void {
+    $this->htmxAttribute->on($event, 'someAction');
+    $rendered = (string) $this->htmxAttribute;
+    $expected .= 'someAction"';
+    // The paths in GitLabCI include a subfolder.
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxOn.
+   *
+   * @return array<int, string[]>
+   *   Array of event, expected.
+   */
+  public static function hxOnDataProvider(): array {
+    return [
+      ['alllowercase', ' data-hx-on-alllowercase="'],
+      ['already-kebab-case', ' data-hx-on-already-kebab-case="'],
+      ['snake_case', ' data-hx-on-snake-case="'],
+      ['camelCaseEvent', ' data-hx-on-camel-case-event="'],
+      ['htmx:beforeRequest', ' data-hx-on-htmx-before-request="'],
+      ['::beforeRequest', ' data-hx-on--before-request="'],
+    ];
+  }
+
+  /**
+   * Test pushUrl method.
+   *
+   * @covers ::pushUrl
+   * @dataProvider hxPushUrlDataProvider
+   */
+  public function testHxPushUrl(bool|Url $value, string $endsWith): void {
+    $startsWith = ' data-hx-push-url="';
+    $this->htmxAttribute->pushUrl($value);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    // So treat all the results as paths.
+    $this->assertStringStartsWith($startsWith, $rendered);
+    $this->assertStringEndsWith($endsWith, $rendered);
+  }
+
+  /**
+   * Test pushUrl method.
+   *
+   * @covers ::pushUrl
+   * @dataProvider hxPushUrlDataProvider
+   */
+  public function testHxReplaceUrl(bool|Url $value, string $endsWith): void {
+    $startsWith = ' data-hx-replace-url="';
+    $this->htmxAttribute->replaceUrl($value);
+    $rendered = (string) $this->htmxAttribute;
+    // The paths in GitLabCI include a subfolder.
+    // So treat all the results as paths.
+    $this->assertStringStartsWith($startsWith, $rendered);
+    $this->assertStringEndsWith($endsWith, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxPushUrl and :testHxReplaceUrl.
+   *
+   * @return array{bool|Url, string}[]
+   *   Array of bool|Url, expected.
+   */
+  public static function hxPushUrlDataProvider(): array {
+    $url = Url::fromRoute('common_test.destination');
+    return [
+      [TRUE, 'true"'],
+      [FALSE, 'false"'],
+      [$url, '/common-test/destination"'],
+    ];
+  }
+
+  /**
+   * Test swapOob method.
+   *
+   * @covers ::swapOob
+   * @dataProvider hxSwapOobDataProvider
+   */
+  public function testHxSwapOob(true|string $value, string $expected): void {
+    $this->htmxAttribute->swapOob($value);
+    $rendered = (string) $this->htmxAttribute;
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxSwapOob.
+   *
+   * @return array{true|string, string}[]
+   *   Array of true|string, expected.
+   */
+  public static function hxSwapOobDataProvider(): array {
+    return [
+      [TRUE, ' data-hx-swap-oob="true"'],
+      ['body:beforeend', ' data-hx-swap-oob="body:beforeend"'],
+    ];
+  }
+
+  /**
+   * Test vals method.
+   *
+   * @covers ::vals
+   */
+  public function testHxVals(): void {
+    $values = ['myValue' => 'My Value'];
+    $this->htmxAttribute->vals($values);
+    $rendered = (string) $this->htmxAttribute;
+    $expected = " data-hx-vals='" . '{"myValue":"My Value"}' . "'";
+    $this->assertEquals($expected, $rendered);
+    // AttributeJson is not tested in AttributeTest, verify safe strings.
+    $values = ['myValue' => '<script>alert(123)</script>'];
+    $this->htmxAttribute->vals($values);
+    $rendered = (string) $this->htmxAttribute;
+    $expected = " data-hx-vals='" . '{"myValue":"alert(123)"}' . "'";
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Test swapOob method.
+   *
+   * @covers ::swapOob
+   * @dataProvider hxBoostDataProvider
+   */
+  public function testHxBoost(bool $value, string $expected): void {
+    $this->htmxAttribute->boost($value);
+    $rendered = (string) $this->htmxAttribute;
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxBoost.
+   *
+   * @return array{bool, string}[]
+   *   Array of bool|string, expected.
+   */
+  public static function hxBoostDataProvider(): array {
+    return [
+      [TRUE, ' data-hx-boost="true"'],
+      [FALSE, ' data-hx-boost="false"'],
+    ];
+  }
+
+  /**
+   * Test headers method.
+   *
+   * @covers ::headers
+   */
+  public function testHxHeaders(): void {
+    $values = ['myValue' => 'My Value'];
+    $this->htmxAttribute->headers($values);
+    $rendered = (string) $this->htmxAttribute;
+    $expected = " data-hx-headers='" . '{"myValue":"My Value"}' . "'";
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Test history method.
+   *
+   * @covers ::history
+   * @dataProvider hxHistoryDataProvider
+   */
+  public function testHxHistory(?bool $value, string $expected): void {
+    if (is_null($value)) {
+      $this->htmxAttribute->history();
+    }
+    else {
+      $this->htmxAttribute->history($value);
+    }
+    $rendered = (string) $this->htmxAttribute;
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxHistory.
+   *
+   * @return array{?bool, string}[]
+   *   Array of null|bool, string, expected.
+   */
+  public static function hxHistoryDataProvider(): array {
+    return [
+      [TRUE, ' data-hx-history="true"'],
+      [FALSE, ' data-hx-history="false"'],
+      [NULL, ' data-hx-history="false"'],
+    ];
+  }
+
+  /**
+   * Test request method.
+   *
+   * @covers ::request
+   */
+  public function testHxRequest(): void {
+    $values = ['timeout' => 100, 'credentials' => FALSE];
+    $this->htmxAttribute->request($values);
+    $rendered = (string) $this->htmxAttribute;
+    $expected = " data-hx-request='" . '{"timeout":100,"credentials":false}' . "'";
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Test swapOob method.
+   *
+   * @covers ::swapOob
+   * @dataProvider hxValidateDataProvider
+   */
+  public function testHxValidate(?bool $value, string $expected): void {
+    if (is_null($value)) {
+      $this->htmxAttribute->validate();
+    }
+    else {
+      $this->htmxAttribute->validate($value);
+    }
+    $rendered = (string) $this->htmxAttribute;
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxHistory.
+   *
+   * @return array{?bool, string}[]
+   *   Array of null|bool, string, expected.
+   */
+  public static function hxValidateDataProvider(): array {
+    return [
+      [TRUE, ' data-hx-validate="true"'],
+      [FALSE, ' data-hx-validate="false"'],
+      [NULL, ' data-hx-validate="true"'],
+    ];
+  }
+
+  /**
+   * Test pushUrl method.
+   *
+   * @covers ::select
+   * @covers ::selectOob
+   * @covers ::swap
+   * @covers ::target
+   * @covers ::trigger
+   * @covers ::confirm
+   * @covers ::disable
+   * @covers ::disabledElements
+   * @covers ::disinherit
+   * @covers ::encoding
+   * @covers ::history
+   * @covers ::historyElement
+   * @covers ::include
+   * @covers ::indicator
+   * @covers ::inherit
+   * @covers ::params
+   * @covers ::preserve
+   * @covers ::prompt
+   * @covers ::sync
+   * @covers \Drupal\Core\Template\AttributeValueBase::render
+   * @dataProvider hxSimpleStringAttributesDataProvider
+   */
+  public function testHxSimpleStringAttributes(string $method, ?string $value, string $expected): void {
+    if (is_null($value)) {
+      $this->htmxAttribute->$method();
+    }
+    else {
+      $this->htmxAttribute->$method($value);
+    }
+    $rendered = (string) $this->htmxAttribute;
+    $this->assertEquals($expected, $rendered);
+  }
+
+  /**
+   * Provides data to ::testHxSimpleStringAttributes.
+   *
+   * @return array{string, string, string}[]
+   *   Array of method, value, expected.
+   */
+  public static function hxSimpleStringAttributesDataProvider(): array {
+    $singleQuotedSyntax = 'info[data-drupal-selector="edit-select"]';
+    return [
+      ['select', '#info-details', ' data-hx-select="#info-details"'],
+      ['select', 'info[data-drupal-selector="edit-select"]', " data-hx-select='$singleQuotedSyntax'"],
+      ['selectOob', '#info-details', ' data-hx-select-oob="#info-details"'],
+      ['selectOob', '#info-details:afterbegin, #alert', ' data-hx-select-oob="#info-details:afterbegin, #alert"'],
+      ['swap', 'afterbegin', ' data-hx-swap="afterbegin  ignoreTitle:true"'],
+      ['target', 'descriptor', ' data-hx-target="descriptor"'],
+      ['trigger', 'event', ' data-hx-trigger="event"'],
+      ['confirm', 'A confirmation message', ' data-hx-confirm="A confirmation message"'],
+      ['disable', NULL, ' data-hx-disable'],
+      ['disabledElements', 'descriptor', ' data-hx-disabled-elt="descriptor"'],
+      ['disinherit', 'descriptor', ' data-hx-disinherit="descriptor"'],
+      ['encoding', NULL, ' data-hx-encoding="multipart/form-data"'],
+      ['encoding', 'application/x-www-form-urlencoded', ' data-hx-encoding="application/x-www-form-urlencoded"'],
+      ['ext', 'name, name', ' data-hx-ext="name, name"'],
+      ['historyElement', NULL, ' data-hx-history-elt'],
+      ['include', 'descriptor', ' data-hx-include="descriptor"'],
+      ['indicator', 'descriptor', ' data-hx-indicator="descriptor"'],
+      ['inherit', 'descriptor', ' data-hx-inherit="descriptor"'],
+      ['params', 'filter string', ' data-hx-params="filter string"'],
+      ['preserve', 'id', ' data-hx-preserve="id"'],
+      ['prompt', 'A prompt message', ' data-hx-prompt="A prompt message"'],
+      ['sync', 'closest form:abort', ' data-hx-sync="closest form:abort"'],
+    ];
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Common/AttributesTest.php b/core/tests/Drupal/Tests/Core/Common/AttributesTest.php
index 6a65be7f0460fe0b3be5eef664db7f0d8a4f3722..9b144858764eb7e8a0c9624af47c6db38d23ba50 100644
--- a/core/tests/Drupal/Tests/Core/Common/AttributesTest.php
+++ b/core/tests/Drupal/Tests/Core/Common/AttributesTest.php
@@ -24,7 +24,7 @@ public static function providerTestAttributeData() {
     return [
       // Verify that special characters are HTML encoded.
       [['&"\'<>' => 'value'], ' &amp;&quot;&#039;&lt;&gt;="value"', 'HTML encode attribute names.'],
-      [['title' => '&"\'<>'], ' title="&amp;&quot;&#039;&lt;&gt;"', 'HTML encode attribute values.'],
+      [['title' => '&"\'<>'], ' title=\'&amp;"\'&lt;&gt;\'', 'XSS filter attribute values.'],
       // Verify multi-value attributes are concatenated with spaces.
       [['class' => ['first', 'last']], ' class="first last"', 'Concatenate multi-value attributes.'],
       // Verify boolean attribute values are rendered correctly.
diff --git a/core/tests/Drupal/Tests/Core/Render/Hypermedia/HtmxOperationsTest.php b/core/tests/Drupal/Tests/Core/Render/Hypermedia/HtmxOperationsTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..1ec2c137bab57d070d2f7c43ee3f80b770e2db91
--- /dev/null
+++ b/core/tests/Drupal/Tests/Core/Render/Hypermedia/HtmxOperationsTest.php
@@ -0,0 +1,102 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\Core\Render\Hypermedia;
+
+use Drupal\Core\Http\HttpMethod;
+use Drupal\Core\Render\Element\RenderElementBase;
+use Drupal\Core\Render\Hypermedia\Htmx;
+use Drupal\Core\Render\Hypermedia\Operations\Insert;
+use Drupal\Core\Render\Hypermedia\Operations\Replace;
+use Drupal\Core\Url;
+use Drupal\Tests\UnitTestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+
+/**
+ * Unit tests for implementations of HtmxOperationInterface.
+ *
+ * @group Hypermedia
+ */
+class HtmxOperationsTest extends UnitTestCase {
+
+  /**
+   * Htmx object to support operation testing.
+   */
+  private Htmx $htmx;
+
+  /**
+   * Tests for HtmxRequestOperationInterface operations need a URL.
+   */
+  private Url|MockObject $url;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->htmx = new Htmx();
+    $this->url = $this->getMockBuilder('\Drupal\Core\Url')
+      ->disableOriginalConstructor()
+      ->onlyMethods(['toString'])
+      ->getMock();
+    $this->url->expects($this->any())
+      ->method('toString')
+      ->willReturn('/example/path');
+  }
+
+  /**
+   * Helper method to process the operations as if the render callback was used.
+   *
+   * @return array
+   *   A stub of a processed render array.
+   */
+  protected function processOperations(): array {
+    return RenderElementBase::processHtmxElement(['#htmx' => $this->htmx]);
+  }
+
+  /**
+   * @covers \Drupal\Core\Render\Hypermedia\Operations\Insert
+   */
+  public function testInsert(): void {
+    $insert = (new Insert())
+      ->select('#source-value')
+      ->target('#target-value')
+      ->setRequest(HttpMethod::Get, $this->url);
+    $this->htmx->setRequestOperation($insert);
+    $result = $this->processOperations();
+    $headers = $result['#attached']['http_header'] ?? [];
+    $attributes = $result['#attributes'] ?? [];
+    $this->assertEquals([], $headers);
+    $expected = [
+      'data-hx-get' => '/example/path',
+      'data-hx-select' => '#source-value',
+      'data-hx-target' => '#target-value',
+      'data-hx-swap' => 'beforeend  ignoreTitle:true',
+    ];
+    $this->assertEquals($expected, $attributes);
+  }
+
+  /**
+   * @covers \Drupal\Core\Render\Hypermedia\Operations\Replace
+   */
+  public function testReplace(): void {
+    $replace = (new Replace())
+      ->select('#source-value')
+      ->target('#target-value')
+      ->setRequest(HttpMethod::Get, $this->url);
+    $this->htmx->setRequestOperation($replace);
+    $result = $this->processOperations();
+    $headers = $result['#attached']['http_header'] ?? [];
+    $attributes = $result['#attributes'] ?? [];
+    $this->assertEquals([], $headers);
+    $expected = [
+      'data-hx-get' => '/example/path',
+      'data-hx-select' => '#source-value',
+      'data-hx-target' => '#target-value',
+      'data-hx-swap' => 'outerHTML  ignoreTitle:true',
+    ];
+    $this->assertEquals($expected, $attributes);
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
index 8f011b46f662a62a452c1095a530f85b2c7564c0..a72c0f34e67c18dd7856f87ebf30e9f72265ea33 100644
--- a/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/AttributeTest.php
@@ -6,6 +6,7 @@
 
 use Drupal\Component\Render\MarkupInterface;
 use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\Xss;
 use Drupal\Core\Render\Markup;
 use Drupal\Core\Template\Attribute;
 use Drupal\Core\Template\AttributeArray;
@@ -379,11 +380,11 @@ public static function providerTestAttributeValues() {
     $data = [];
 
     $string = '"> <script>alert(123)</script>"';
-    $data['safe-object-xss1'] = [['title' => Markup::create($string)], ' title="&quot;&gt; alert(123)&quot;"'];
-    $data['non-safe-object-xss1'] = [['title' => $string], ' title="' . Html::escape($string) . '"'];
+    $data['safe-object-xss1'] = [['title' => Markup::create($string)], ' title=\'"&gt; alert(123)"\''];
+    $data['non-safe-object-xss1'] = [['title' => $string], ' title=\'' . Xss::filter($string) . "'"];
     $string = '&quot;><script>alert(123)</script>';
-    $data['safe-object-xss2'] = [['title' => Markup::create($string)], ' title="&quot;&gt;alert(123)"'];
-    $data['non-safe-object-xss2'] = [['title' => $string], ' title="' . Html::escape($string) . '"'];
+    $data['safe-object-xss2'] = [['title' => Markup::create($string)], ' title=\'"&gt;alert(123)\''];
+    $data['non-safe-object-xss2'] = [['title' => $string], ' title="' . Xss::filter($string) . '"'];
 
     return $data;
   }
diff --git a/core/themes/claro/claro.theme b/core/themes/claro/claro.theme
index c406fed47c22b286d4c074bd10eaeb8f5e55ceb1..05409f13e5ab36b56f813a28e9e410d81270e784 100644
--- a/core/themes/claro/claro.theme
+++ b/core/themes/claro/claro.theme
@@ -14,6 +14,7 @@
 use Drupal\Core\Link;
 use Drupal\Core\Render\Element;
 use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\HtmlAttributeInterface;
 use Drupal\Core\Url;
 use Drupal\media\MediaForm;
 use Drupal\file\FileInterface;
@@ -725,7 +726,7 @@ function claro_form_menu_link_content_form_alter(&$form, FormStateInterface $for
       '#group' => 'advanced',
       '#title' => t('Description'),
       '#attributes' => ['class' => ['entity-meta__description']],
-      '#tree' => FALSE,
+      '#tree' => TRUE,
       '#accordion' => TRUE,
       'description' => $form['description'],
     ];
@@ -1270,7 +1271,7 @@ function claro_preprocess_system_themes_page(&$variables): void {
           // @todo Remove dependency on attributes after
           //   https://www.drupal.org/project/drupal/issues/2511548 has been
           //   resolved.
-          if (isset($theme_card['screenshot']['#attributes']) && $theme_card['screenshot']['#attributes'] instanceof Attribute && $theme_card['screenshot']['#attributes']->hasClass('no-screenshot')) {
+          if (isset($theme_card['screenshot']['#attributes']) && $theme_card['screenshot']['#attributes'] instanceof HtmlAttributeInterface && $theme_card['screenshot']['#attributes']->hasClass('no-screenshot')) {
             unset($theme_card['screenshot']);
           }
 
diff --git a/core/themes/olivero/olivero.theme b/core/themes/olivero/olivero.theme
index d10ee7d155cd78cb7f3fbf8e22252787f801e572..35e1d59092e108386f4b73ef1e3f67343fd6ee8c 100644
--- a/core/themes/olivero/olivero.theme
+++ b/core/themes/olivero/olivero.theme
@@ -608,7 +608,7 @@ function olivero_preprocess_table(&$variables): void {
   if (!empty($variables['rows'])) {
     $draggable_row_found = FALSE;
     foreach ($variables['rows'] as &$row) {
-      /** @var \Drupal\Core\Template\Attribute $row['attributes'] */
+      /** @var \Drupal\Core\Template\Attribute $row ['attributes'] */
       if (!empty($row['attributes']) && $row['attributes']->hasClass('draggable')) {
         if (!$draggable_row_found) {
           $variables['attributes']['class'][] = 'draggable-table';