Docs: Document the `$page_hook` action.

Props johnbillion.
Fixes #43643.


Built from https://develop.svn.wordpress.org/trunk@44501


git-svn-id: http://core.svn.wordpress.org/trunk@44332 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/admin.php

@@ -234,7 +234,18 @@ if ( isset( $plugin_page ) ) {
 		/**
 		 * Used to call the registered callback for a plugin screen.
 		 *
-		 * @ignore
+		 * This hook uses a dynamic hook name, `$page_hook`, which refers to a mixture of plugin
+		 * page information including:
+		 * 1. The page type. If the plugin page is registered as a submenu page, such as for
+		 *    Settings, the page type would be 'settings'. Otherwise the type is 'toplevel'.
+		 * 2. A separator of '_page_'.
+		 * 3. The plugin basename minus the file extension.
+		 *
+		 * Together, the three parts form the `$page_hook`. Citing the example above,
+		 * the hook name used would be 'settings_page_pluginbasename'.
+		 *
+		 * @see get_plugin_page_hook()
+		 *
 		 * @since 1.5.0
 		 */
 		do_action( $page_hook );

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44500';
+$wp_version = '5.1-alpha-44501';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.