code: function onUnFold(cm, from, to) {
          var state = cm.state.foldGutter;
          var vp = cm.getViewport();
          delete cm._lineFolds[from.line];
          updateFoldInfo(cm, from.line, to.line || vp.to);
      }
docs: Triggered when a folded code segment is unfolded.
  @param {!CodeMirror} cm the CodeMirror instance for the active editor
  @param {!{line:number, ch:number}} from  the ch and line position that designates the start of the region
  @param {!{line:number, ch:number}} to the ch and line position that designates the end of the region