docs: function toReqExpAction( action ) {
          var list;
  
          if ( action === undefined ) {
              return;
          }
  
          if ( type.call( action, 'RegExp' ) ) {
              return action;
          }
  
          list = action.split(' ');
  
          list.map(function( item ) {
              return stringToRegExp( item );
          });
  
          return new RegExp( '(^|\\s)(' + list.join('|') + ')($|\\s|\\.)' );
      }