twentynineteen_add_dropdown_icons( string $item_output, WP_Post $item, int $depth, stdClass $args ): string

72function twentynineteen_add_dropdown_icons( $item_output, $item, $depth, $args ) {73 74	// Only add class to 'top level' items on the 'primary' menu.75	if ( ! isset( $args->theme_location ) || 'menu-1' !== $args->theme_location ) {76		return $item_output;77	}78 79	if ( in_array( 'mobile-parent-nav-menu-item', $item->classes, true ) && isset( $item->original_id ) ) {80		// Inject the keyboard_arrow_left SVG inside the parent nav menu item, and let the item link to the parent item.81		// @todo Only do this for nested submenus? If on a first-level submenu, then really the link could be "#" since the desire is to remove the target entirely.82		$link = sprintf(83			'<button class="menu-item-link-return" tabindex="-1">%s',84			twentynineteen_get_icon_svg( 'chevron_left', 24 )85		);86 87		// Replace opening <a> with <button>.88		$item_output = preg_replace(89			'/<a\s.*?>/',90			$link,91			$item_output,92			1 // Limit.93		);94 95		// Replace closing </a> with </button>.96		$item_output = preg_replace(97			'#</a>#i',98			'</button>',99			$item_output,100			1 // Limit.101		);102 103	} elseif ( in_array( 'menu-item-has-children', $item->classes, true ) ) {104 105		// Add SVG icon to parent items.106		$icon = twentynineteen_get_icon_svg( 'keyboard_arrow_down', 24 );107 108		$item_output .= sprintf(109			'<button class="submenu-expand" tabindex="-1">%s</button>',110			$icon111		);112	}113 114	return $item_output;115}