code: function () {
                  var e, expressions = [];
  
                  do {
                      e = this.expression();
                      if (e) {
                          expressions.push(e);
                          if (! $char(',')) { break; }
                      }
                  } while(e);
  
                  if (expressions.length > 0) {
                      return new(tree.Value)(expressions);
                  }
              }
docs: A Value is a comma-delimited list of Expressions  font-family: Baskerville, Georgia, serif;  In a Rule, a Value represents everything after the `:`, and before the `;`.