From 8ba2f37e966d262d9ba32d7901a422fec58a33cd Mon Sep 17 00:00:00 2001
From: Faisal Ahammad <faisalahammad24@gmail.com>
Date: Tue, 9 Sep 2025 11:22:10 +0600
Subject: [PATCH] Preserve custom HTML for unfiltered users in classic editor

Adds a filter to allow all elements and attributes in TinyMCE for users with the 'unfiltered_html' capability when using the classic editor. This prevents TinyMCE from stripping custom HTML elements when switching between Text and Visual modes, addressing issues for advanced users while maintaining default sanitization for others.
---
 classic-editor.php | 100 +++++++++++++++++++++++++++++++++++----------
 1 file changed, 79 insertions(+), 21 deletions(-)

diff --git a/classic-editor.php b/classic-editor.php
index 293d362..de9d64f 100644
--- a/classic-editor.php
+++ b/classic-editor.php
@@ -136,15 +136,20 @@ public static function init_actions() {
 			// Move the Privacy Page notice back under the title.
 			add_action( 'admin_init', array( __CLASS__, 'on_admin_init' ) );
 		}
-		if ( $gutenberg ) {
-			// These are handled by this plugin. All are older, not used in 5.3+.
-			remove_action( 'admin_init', 'gutenberg_add_edit_link_filters' );
-			remove_action( 'admin_print_scripts-edit.php', 'gutenberg_replace_default_add_new_button' );
-			remove_filter( 'redirect_post_location', 'gutenberg_redirect_to_classic_editor_when_saving_posts' );
-			remove_filter( 'display_post_states', 'gutenberg_add_gutenberg_post_state' );
-			remove_action( 'edit_form_top', 'gutenberg_remember_classic_editor_when_saving_posts' );
-		}
-	}
+		if ( $gutenberg ) {
+			// These are handled by this plugin. All are older, not used in 5.3+.
+			remove_action( 'admin_init', 'gutenberg_add_edit_link_filters' );
+			remove_action( 'admin_print_scripts-edit.php', 'gutenberg_replace_default_add_new_button' );
+			remove_filter( 'redirect_post_location', 'gutenberg_redirect_to_classic_editor_when_saving_posts' );
+			remove_filter( 'display_post_states', 'gutenberg_add_gutenberg_post_state' );
+			remove_action( 'edit_form_top', 'gutenberg_remember_classic_editor_when_saving_posts' );
+		}
+
+		// Preserve custom HTML elements for users allowed to post unfiltered HTML
+		// when using the classic editor (prevents TinyMCE from stripping elements
+		// on Text ⇄ Visual switches).
+		add_filter( 'tiny_mce_before_init', array( __CLASS__, 'allow_custom_elements_for_unfiltered' ), 20 );
+	}
 
 	public static function remove_gutenberg_hooks( $remove = 'all' ) {
 		remove_action( 'admin_menu', 'gutenberg_menu' );
@@ -1017,17 +1022,70 @@ public static function replace_post_js( $scripts ) {
 	 * See: https://core.trac.wordpress.org/ticket/62504 and 
 	 * https://github.com/WordPress/classic-editor/issues/222.
 	 */
-	public static function replace_post_js_2( $src, $handle ) {
-		if ( 'post' === $handle && is_string( $src ) && false === strpos( $src, 'ver=62504-20241121' ) ) {
-			$suffix = wp_scripts_get_suffix();
-			$src    = plugins_url( 'scripts/', __FILE__ ) . "post{$suffix}.js";
-			$src    = add_query_arg( 'ver', '62504-20241121', $src );
-		}
-
-		return $src;
-	}
-}
-
-add_action( 'plugins_loaded', array( 'Classic_Editor', 'init_actions' ) );
+	public static function replace_post_js_2( $src, $handle ) {
+		if ( 'post' === $handle && is_string( $src ) && false === strpos( $src, 'ver=62504-20241121' ) ) {
+			$suffix = wp_scripts_get_suffix();
+			$src    = plugins_url( 'scripts/', __FILE__ ) . "post{$suffix}.js";
+			$src    = add_query_arg( 'ver', '62504-20241121', $src );
+		}
+
+		return $src;
+	}
+
+	/**
+	 * Allow all elements/attributes in TinyMCE for users with `unfiltered_html`
+	 * while editing in the classic editor. This prevents stripping of custom
+	 * elements when switching between Text and Visual modes. Does not affect
+	 * users without this capability, preserving default sanitization expectations.
+	 *
+	 * @param array $init TinyMCE init settings.
+	 * @return array Possibly adjusted init settings.
+	 */
+	public static function allow_custom_elements_for_unfiltered( $init ) {
+		if ( ! is_admin() || ! current_user_can( 'unfiltered_html' ) ) {
+			return $init;
+		}
+
+		// Apply only on classic editor screens to avoid unintended side effects.
+		$apply = false;
+		$post_id = self::get_edited_post_id();
+		$settings = self::get_settings();
+
+		// Attempt to reliably detect the classic editor context.
+		if ( function_exists( 'get_current_screen' ) ) {
+			$screen = get_current_screen();
+			if ( isset( $screen->base ) && 'post' === $screen->base ) {
+				if ( $post_id ) {
+					$apply = ( 'classic' === $settings['editor'] || self::is_classic( $post_id ) );
+				} else {
+					// On Add New when classic is default and not switching to block.
+					$apply = ( 'classic' === $settings['editor'] && ! isset( $_GET['classic-editor__forget'] ) ); // phpcs:ignore WordPress.Security.NonceVerification.Recommended
+				}
+			}
+		}
+
+		if ( ! $apply ) {
+			return $init;
+		}
+
+		// Ensure extended elements and children allow any element/attributes.
+		// Keeps unknown/custom tags intact during TinyMCE processing for these users.
+		if ( empty( $init['extended_valid_elements'] ) ) {
+			$init['extended_valid_elements'] = '*[*]';
+		} else {
+			$init['extended_valid_elements'] .= ',*[*]';
+		}
+
+		if ( empty( $init['valid_children'] ) ) {
+			$init['valid_children'] = '+*[*]';
+		} else {
+			$init['valid_children'] .= ',+*[*]';
+		}
+
+		return $init;
+	}
+}
+
+add_action( 'plugins_loaded', array( 'Classic_Editor', 'init_actions' ) );
 
 endif;