code: function setActivePaneId(newPaneId) {
          if (!_isSpecialPaneId(newPaneId) && newPaneId !== _activePaneId) {
              var oldPaneId = _activePaneId,
                  oldPane = _getPane(ACTIVE_PANE),
                  newPane = _getPane(newPaneId);
  
              if (!newPane) {
                  throw new Error("invalid pane id: " + newPaneId);
              }
  
              _activePaneId = newPaneId;
  
              exports.trigger("activePaneChange", newPaneId, oldPaneId);
              exports.trigger("currentFileChange", _getPane(ACTIVE_PANE).getCurrentlyViewedFile(),
                                                              newPaneId,
                                                              oldPane.getCurrentlyViewedFile(),
                                                              oldPaneId);
  
              _makePaneMostRecent(_activePaneId);
              focusActivePane();
          }
      }
docs: Switch active pane to the specified pane id (or ACTIVE_PANE/ALL_PANES, in which case this
  call does nothing).
  @param {!string} paneId - the id of the pane to activate