docs: function (mml) {
        if (mml.complexity > this.COLLAPSE.relseq) {
          var content = this.SplitAttribute(mml,"content");
          var marker = Collapsible.FindChildText(mml,content[0]);
          if (content.length > 1) marker += "\u22EF";
          mml = this.MakeAction(this.Marker(marker),mml);
        }
        return mml;
      }