Docs: Document the $id parameter for Walker_CategoryDropdown::start_el(), which is implemented by Walker but unused in the subclass method.

See #32246.


git-svn-id: https://develop.svn.wordpress.org/trunk@35926 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-walker-category-dropdown.php

@@ -41,6 +41,7 @@ class Walker_CategoryDropdown extends Walker {
 	 * @param int    $depth    Depth of category. Used for padding.
 	 * @param array  $args     Uses 'selected', 'show_count', and 'value_field' keys, if they exist.
 	 *                         See {@see wp_dropdown_categories()}.
+	 * @param int    $id       Optional. ID of the current category. Default 0 (unused).
 	 */
 	public function start_el( &$output, $category, $depth = 0, $args = array(), $id = 0 ) {
 		$pad = str_repeat(' ', $depth * 3);