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filter is not described

walker_nav_menu_start_el filter-hook . WP 3.0.0

Filters a menu item's starting output.

The menu item's starting output only includes $args->before, the opening <a>, the menu item's title, the closing </a>, and $args->after. Currently, there is no filter for modifying the opening and closing <li> for a menu item.

Usage

add_filter( 'walker_nav_menu_start_el', 'filter_function_name_2012', 10, 4 );
function filter_function_name_2012( $item_output, $item, $depth, $args ){
	// filter...

	return $item_output;
}
$item_output(string)
The menu item's starting HTML output.
$item(WP_Post)
Menu item data object.
$depth(int)
Depth of menu item. Used for padding.
$args(stdClass)
An object of wp_nav_menu() arguments.

Where the hook is called

Walker_Nav_Menu::start_el()
walker_nav_menu_start_el
wp-includes/class-walker-nav-menu.php 238
$output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );

Where the hook is used (in WP core)

Does not used.