Brad Jones
--- a/core/lib/Drupal/Core/Render/Element/Url.php
+++ b/core/lib/Drupal/Core/Render/Element/Url.php
    $value = trim($element['#value']);
    $form_state->setValueForElement($element, $value);

-    if ($value !== '' && !UrlHelper::isValid($value, TRUE)) {
-      $form_state->setError($element, t('The URL %url is not valid.', ['%url' => $value]));
+    if ($value !== '') {
+      if ($element['#require_url'] && !UrlHelper::isValid($value, TRUE)) {
+        $form_state->setError($element, t('The URL %url is not valid.', ['%url' => $value]));
+      }
+      elseif (!UrlHelper::validateUri($value)) {
+        $form_state->setError($element, t('The URI %uri is not valid.', ['%uri' => $value]));
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
    // - That it is well formed (parse_url() returns FALSE if not).
    // - That it contains a scheme (parse_url(, PHP_URL_SCHEME) returns NULL if
    //   not).
-    if ($typed_data instanceof UriInterface && in_array(parse_url($value, PHP_URL_SCHEME), [NULL, FALSE], TRUE)) {
+    if ($typed_data instanceof UriInterface && !UrlHelper::validateUri($value)) {
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/UriWidget.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldWidget/UriWidget.php
    return [
      'size' => 60,
      'placeholder' => '',
+      'require_url' => TRUE,
--- a/core/lib/Drupal/Component/Utility/UrlHelper.php
+++ b/core/lib/Drupal/Component/Utility/UrlHelper.php
+          | (?:[A-Za-z0-9\-._~!$&'()*+,;=]|%[0-9A-Fa-f]{2})*
+          )
+          (?: : [0-9]* )?
+          (?:\/ (?:[A-Za-z0-9\-._~!$&'()*+,;=:@]|%[0-9A-Fa-f]{2})* )*
+        | \/
+          (?:    (?:[A-Za-z0-9\-._~!$&'()*+,;=:@]|%[0-9A-Fa-f]{2})+
+            (?:\/ (?:[A-Za-z0-9\-._~!$&'()*+,;=:@]|%[0-9A-Fa-f]{2})* )*
+          )?
+        |        (?:[A-Za-z0-9\-._~!$&'()*+,;=@] |%[0-9A-Fa-f]{2})+
+            (?:\/ (?:[A-Za-z0-9\-._~!$&'()*+,;=:@]|%[0-9A-Fa-f]{2})* )*
+        |
+        )
+        (?:\? (?:[A-Za-z0-9\-._~!$&'()*+,;=:@\/?]|%[0-9A-Fa-f]{2})* )?
+        (?:\# (?:[A-Za-z0-9\-._~!$&'()*+,;=:@\/?]|%[0-9A-Fa-f]{2})* )?
+      )$/x";
+    return preg_match($regex, $value);