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WordPress

Walker_Nav_Menu::start_lvl( string $output, int $depth = 0, stdClass $args = null )

Since
3.0.0
Source
wp-includes/class-walker-nav-menu.php:70
Starts the list before the elements are added.

Compatibility

WordPress
since 3.0.0
PHP
7.4–8.6-dev
  • 6.7.7
  • 6.8.8
  • 6.9.7
  • 7.0.4
  • 7.1.0

Present in every tracked release (6.7.7 to 7.1.0), and compiles on PHP 7.4 through 8.6-dev.

Parameters

$outputstring
Used to append additional content (passed by reference).
$depthintoptional
Depth of menu item. Used for padding.Default: 0
$argsstdClassoptional
An object of wp_nav_menu() arguments.Default: null

Performance profile

How much work a call to Walker_Nav_Menu::start_lvl() does, and what it touches: the algorithmic scaling, the Zend instruction count per call across PHP versions, the hooks it hands control to, and the core code that calls it. Measured from the compiled opcodes, not a stopwatch, so every number is identical on any machine running the same PHP version, and every function in core is ranked by cost.

Cost class
Trivial

Touches nothing outside its own arguments.

Scaling
Constant

No loop in the body: the same number of instructions runs whatever you pass in.

Instructions
45–50

Executed per call on PHP 8.5, depending on the branch taken. The body compiles to 53.

Plugin surface
2 hooks

Third-party callbacks on 'nav_menu_submenu_css_class', 'nav_menu_submenu_attributes' run inside this call, and their cost is not bounded by anything here.

Called by
0

Nothing in core calls this; the cost is only what you spend yourself.

What it touches

  • hookthird-party callbacksapply_filters()called directly

What one call costs · 1 distinct outcome

One number would be a lie: the work depends on which branch runs. These are every distinct cost Walker_Nav_Menu::start_lvl() can have, taken from its control-flow graph on PHP 8.5.

WhenInstructionsCalls it makes
always45–50str_repeat(), apply_filters(), apply_filters(), ->build_atts()

Across PHP versions

PHPCompiledExecutedBranchesNotes
8.6-dev5345–503
8.55345–503
8.45345–5034 fewer instructions than PHP 8.3
8.35749–543
8.25749–543
8.15749–543
7.45749–543

An instruction is not a fixed amount of time, so a matching count is not necessarily the same speed; what it rules out is a difference in the work itself.

Hooks and filters fired · 2

2 hooks fire while Walker_Nav_Menu::start_lvl() runs, in this order:

  1. apply_filters( nav_menu_submenu_css_class )filterline 92 (+22 into the body)

    Filters the CSS class(es) applied to a menu list element.

  2. apply_filters( nav_menu_submenu_attributes )filterline 110 (+40 into the body)

    Filters the HTML attributes applied to a menu list element.

Uses · 2

Source code

	public function start_lvl( &$output, $depth = 0, $args = null ) {		if ( isset( $args->item_spacing ) && 'discard' === $args->item_spacing ) {			$t = '';			$n = '';		} else {			$t = "\t";			$n = "\n";		}		$indent = str_repeat( $t, $depth ); 		// Default class.		$classes = array( 'sub-menu' ); 		/**		 * Filters the CSS class(es) applied to a menu list element.		 *		 * @since 4.8.0		 *		 * @param string[] $classes Array of the CSS classes that are applied to the menu `<ul>` element.		 * @param stdClass $args    An object of `wp_nav_menu()` arguments.		 * @param int      $depth   Depth of menu item. Used for padding.		 */		$class_names = implode( ' ', apply_filters( 'nav_menu_submenu_css_class', $classes, $args, $depth ) ); 		$atts          = array();		$atts['class'] = ! empty( $class_names ) ? $class_names : ''; 		/**		 * Filters the HTML attributes applied to a menu list element.		 *		 * @since 6.3.0		 *		 * @param array $atts {		 *     The HTML attributes applied to the `<ul>` element, empty strings are ignored.		 *		 *     @type string $class    HTML CSS class attribute.		 * }		 * @param stdClass $args      An object of `wp_nav_menu()` arguments.		 * @param int      $depth     Depth of menu item. Used for padding.		 */		$atts       = apply_filters( 'nav_menu_submenu_attributes', $atts, $args, $depth );		$attributes = $this->build_atts( $atts ); 		$output .= "{$n}{$indent}<ul{$attributes}>{$n}";	}

Changelog

Introduced in 3.0.0. Unchanged from 6.7.7 through 7.1.0.

  1. 6.7.7
  2. 6.8.8
  3. 6.9.7
  4. 7.0.4
  5. 7.1.0

Signature, return type and hooks compared across 5 parsed releases.

About this page

Parsed data
Generated from the wordpress-develop 7.1.0 tag, from src/wp-includes/class-walker-nav-menu.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.
Corrections
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