code: function onFold(cm, from, to) {
          var state = cm.state.foldGutter;
          updateFoldInfo(cm, from.line, from.line + 1);
      }
docs: Triggered when a code segment is folded.
  @param {!CodeMirror} cm the CodeMirror instance for the active editor
  @param {!Object} from  the ch and line position that designates the start of the region
  @param {!Object} to the ch and line position that designates the end of the region