in case mark_grp() gets only a single group, we fall-back to the default/simple mark()
in case mark_grp() gets only a single group, we fall-back to the default/simple mark()

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb