docs: public int bookmarkToIndex(Object bookmark, int iHandleType)
      {
          if (bookmark == null)
              return -1;
          int iTargetPosition = m_gridBuffer.bookmarkToIndex(bookmark, iHandleType);
          if (iTargetPosition == -1)
              iTargetPosition = m_gridList.bookmarkToIndex(bookmark, iHandleType);
          return iTargetPosition;   // Target position
      }