code: function _LayoutCommon_initialize(site, groupsEnabled) {
                      site._writeProfilerMark("Layout:initialize,info");
                      if (!this._inListMode) {
                          _ElementUtilities.addClass(site.surface, _Constants._gridLayoutClass);
                      }
  
                      if (this._backdropColorClassName) {
                          _ElementUtilities.addClass(site.surface, this._backdropColorClassName);
                      }
                      if (this._disableBackdropClassName) {
                          _ElementUtilities.addClass(site.surface, this._disableBackdropClassName);
                      }
                      this._groups = [];
                      this._groupMap = {};
                      this._oldGroupHeaderPosition = null;
                      this._usingStructuralNodes = false;
  
                      this._site = site;
                      this._groupsEnabled = groupsEnabled;
                      this._resetAnimationCaches(true);
                  }
docs: Implementation of part of ILayout interface