diff --git a/src/backend/utils/cache/relcache.c b/src/backend/utils/cache/relcache.c
index 8e28335915f..8e08ca1c680 100644
--- a/src/backend/utils/cache/relcache.c
+++ b/src/backend/utils/cache/relcache.c
@@ -5150,9 +5150,15 @@ RelationGetIndexPredicate(Relation relation)
  * simple index keys, but attributes used in expressions and partial-index
  * predicates.)
  *
- * Depending on attrKind, a bitmap covering the attnums for all index columns,
- * for all potential foreign key columns, or for all columns in the configured
- * replica identity index is returned.
+ * Depending on attrKind, a bitmap covering attnums for certain columns is
+ * returned:
+ *	INDEX_ATTR_BITMAP_KEY			Columns in non-partial unique indexes not
+ *									in expressions (i.e., usable for FKs)
+ *	INDEX_ATTR_BITMAP_PRIMARY_KEY	Columns in the table's primary key
+ *	INDEX_ATTR_BITMAP_IDENTITY_KEY	Columns in the table's replica identity
+ *									index (empty if FULL)
+ *	INDEX_ATTR_BITMAP_HOT_BLOCKING	Columns that block updates from being HOT
+ *	INDEX_ATTR_BITMAP_SUMMARIZED	Columns included in summarizing indexes
  *
  * Attribute numbers are offset by FirstLowInvalidHeapAttributeNumber so that
  * we can include system attributes (e.g., OID) in the bitmap representation.
diff --git a/src/include/utils/relcache.h b/src/include/utils/relcache.h
index beeb28b83cb..38524641f47 100644
--- a/src/include/utils/relcache.h
+++ b/src/include/utils/relcache.h
@@ -54,6 +54,9 @@ extern List *RelationGetIndexPredicate(Relation relation);
 extern Datum *RelationGetIndexRawAttOptions(Relation indexrel);
 extern bytea **RelationGetIndexAttOptions(Relation relation, bool copy);
 
+/*
+ * Which set of columns to return by RelationGetIndexAttrBitmap.
+ */
 typedef enum IndexAttrBitmapKind
 {
 	INDEX_ATTR_BITMAP_KEY,