Issue #2320111 by Wim Leers | mparker17: Better help text for the "Alternative...

Issue #2320111 by Wim Leers | mparker17: Better help text for the "Alternative text" field in the Text Editor image dialog.

core/modules/editor/src/Form/EditorImageDialog.php

@@ -108,6 +108,7 @@ public function buildForm(array $form, FormStateInterface $form_state, FilterFor
     }
     $form['attributes']['alt'] = array(
       '#title' => $this->t('Alternative text'),
+      '#placeholder' => $this->t('Short description for the visually impaired'),
       '#type' => 'textfield',
       '#required' => TRUE,
       '#required_error' => $this->t('Alternative text is required.<br><em>(Only in rare cases should this be left empty. To create empty alternative text, enter <code>""</code> — two double quotes without any content).'),