KSES: Document HTML allow list is in lowercase.

Expand documentation of the `wp_kses_allowed_html` hook to indicate that developers must add permitted HTML tags and attributes in lowercase for KSES to recognise they are permitted.

Props r-a-y, SergeyBiryukov, peterwilsoncc.
Fixes #55407.
See #53399.


Built from https://develop.svn.wordpress.org/trunk@53034


git-svn-id: http://core.svn.wordpress.org/trunk@52623 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/kses.php

@@ -820,6 +820,10 @@ function wp_kses_allowed_html( $context = '' ) {
 		/**
 		 * Filters the HTML tags that are allowed for a given context.
 		 *
+		 * HTML tags and attribute names are case-insensitive in HTML but must be
+		 * added to the KSES allow list in lowercase. An item added to the allow list
+		 * in upper or mixed case will not recognized as permitted by KSES.
+		 *
 		 * @since 3.5.0
 		 *
 		 * @param array[] $html    Allowed HTML tags.

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-53033';
+$wp_version = '6.0-alpha-53034';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.