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Edit File: class-wp-customize-nav-menu-section.php
<?php /** * Customize API: WP_Customize_Nav_Menu_Section class * * @package WordPress * @subpackage Customize * @since 4.4.0 */ /** * Customize Menu Section Class * * Custom section only needed in JS. * * @since 4.3.0 * * @see WP_Customize_Section */ class WP_Customize_Nav_Menu_Section extends WP_Customize_Section { /** * Control type. * * @since 4.3.0 * @var string */ public $type = 'nav_menu'; /** * Get section parameters for JS. * * @since 4.3.0 * @return array Exported parameters. */ public function json() { $exported = parent::json(); $exported['menu_id'] = (int) preg_replace( '/^nav_menu\[(-?\d+)\]/', '$1', $this->id ); return $exported; } }