code: function () {
                      var k;
  
                      k = $re(/^[_A-Za-z-][_A-Za-z0-9-]*/);
                      if (k) {
                          var color = tree.Color.fromKeyword(k);
                          if (color) {
                              return color;
                          }
                          return new(tree.Keyword)(k);
                      }
                  }
docs: A catch-all word, such as:  black border-collapse