code: function addListToWorkingSet(paneId, fileList) {
          var uniqueFileList,
              pane = _getPane(paneId);
  
          uniqueFileList = pane.addListToViewList(fileList);
  
          uniqueFileList.forEach(function (file) {
              if (_findFileInMRUList(pane.id, file) !== -1) {
                  console.log(file.fullPath + " duplicated in mru list");
              }
              _mruList.push(_makeMRUListEntry(file, pane.id));
          });
  
          exports.trigger("workingSetAddList", uniqueFileList, pane.id);
  
          //  find all of the files that could be added but were not
          var unsolvedList = fileList.filter(function (item) {
              // if the file open in another pane, then add it to the list of unsolvedList
              return (pane.findInViewList(item.fullPath) === -1 && _getPaneIdForPath(item.fullPath));
          });
  
          // Use the pane id of the first one in the list for pane id and recurse
          //  if we add more panes, then this will recurse until all items in the list are satisified
          if (unsolvedList.length) {
              addListToWorkingSet(_getPaneIdForPath(unsolvedList[0].fullPath), unsolvedList);
          }
      }
docs: Adds the given file list to the end of the workingset.
  @param {!string} paneId - The id of the pane in which to add the file object to or ACTIVE_PANE
  @param {!Array.<File>} fileList - Array of files to add to the pane