code: function setRTLFlagOnCSSLink( url, isRTL ) {
  	if ( isRTL ) {
  		return url.endsWith( '.rtl.css' ) ? url : url.replace( /\.css$/, '.rtl.css' );
  	}
  
  	return ! url.endsWith( '.rtl.css' ) ? url : url.replace( /\.rtl.css$/, '.css' );
  }
docs: /*
  CSS links come in two flavors: either RTL stylesheets with `.rtl.css` suffix, or LTR ones
  with `.css` suffix. This function sets a desired `isRTL` flag on the supplied URL, i.e., it
  changes the extension if necessary.