code: function tokenComment(stream, state) {
      var maybeEnd = false, maybeNested = false, nestedCount = 0, ch;
      while (ch = stream.next()) {
        if (ch == ")" && maybeEnd) {
          if(nestedCount > 0)
            nestedCount--;
          else {
            popStateStack(state);
            break;
          }
        }
        else if(ch == ":" && maybeNested) {
          nestedCount++;
        }
        maybeEnd = (ch == ":");
        maybeNested = (ch == "(");
      }
      
      return ret("comment", "comment");
    }
docs: handle comments, including nested