code: function(record, e, keepExisting) {
          var me = this,
              isSelected = me.isSelected(record);
  
          switch (me.selectionMode) {
              case 'MULTI':
                  if (e.shiftKey && me.selectionStart) {
                      me.selectRange(me.selectionStart, record, e.ctrlKey);
                  } else if (e.ctrlKey && isSelected) {
                      me.doDeselect(record, false);
                  } else if (e.ctrlKey) {
                      me.doSelect(record, true, false);
                  } else if (isSelected && !e.shiftKey && !e.ctrlKey && me.selected.getCount() > 1) {
                      me.doSelect(record, keepExisting, false);
                  } else if (!isSelected) {
                      me.doSelect(record, false);
                  }
                  break;
              case 'SIMPLE':
                  if (isSelected) {
                      me.doDeselect(record);
                  } else {
                      me.doSelect(record, true);
                  }
                  break;
              case 'SINGLE':
                  // if allowDeselect is on and this record isSelected, deselect it
                  if (me.allowDeselect && isSelected) {
                      me.doDeselect(record);
                  // select the record and do NOT maintain existing selections
                  } else {
                      me.doSelect(record, false);
                  }
                  break;
          }
  
          // selectionStart is a start point for shift/mousedown to create a range from.
          // If the mousedowned record was not already selected, then it becomes the
          // start of any range created from now on.
          // If we drop to no records selected, then there is no range start any more.
          if (!e.shiftKey) {
              if (me.isSelected(record)) {
                  me.selectionStart = record;
              } else {
                  me.selectionStart = null;
              }
          }
      }
docs: Provides differentiation of logic between MULTI, SIMPLE and SINGLE selection modes. Requires that an event be passed so that we can know if user held ctrl or shift.