When would the function group.multicolumn() used?

Hi all, I found the following new MAL function in the new release of version 11.23.3: ============================================================ pattern group.multicolumn(b:bat[:any]...) (ref:bat[:oid],grp:bat[:oid],hist:bat[:any]) address GROUPmulticolumngroup; comment Derivation of a group index over multiple columns. ============================================================ I thought I may be used by queries with multiple attributes in the GROUP BY clause. So I tried to EXPLAIN such a query (e.g., SELECT ... FROM... GROUP BY ColA, ColB), but it is still compiled with multiple group.subgroup() followed by a group.subgroupdone(). So, when would this function group.multicolumn() used? Thanks, Wenjian