public static function extend( $placeholder, array $selectors ) {
		if ( ! isset( static::$placeholders[ $placeholder ] ) ) {
			static::$placeholders[ $placeholder ] = [];
		}

		static::$placeholders[ $placeholder ] = array_merge(
			static::$placeholders[ $placeholder ],
			$selectors
		);
	}
public static function extend( $placeholder, array $selectors ) {
		if ( ! isset( static::$placeholders[ $placeholder ] ) ) {
			static::$placeholders[ $placeholder ] = [];
		}

		static::$placeholders[ $placeholder ] = array_merge(
			static::$placeholders[ $placeholder ],
			$selectors
		);
	}
public static function extend ( $ placeholder , array $ selectors ) { if ( ! isset ( static :: $ placeholders [ $ placeholder ] ) ) { static :: $ placeholders [ $ placeholder ] = [ ] ; } static :: $ placeholders [ $ placeholder ] = array_merge ( static :: $ placeholders [ $ placeholder ] , $ selectors ) ; }
Set selectors. Styles of these selectors output like extend of Sass.

@param string $placeholder
@param array $selectors
@return void
Set selectors . Styles of these selectors output like extend of Sass .