-If prefix argument CHILDREN is given, promote also all the children.
-If the region is active in `transient-mark-mode', promote all headings
-in the region."
+If transient-mark-mode is on, and mark is active, promote headings in
+the region (from a Lisp program, pass `region' for WHICH). Otherwise:
+without prefix argument, promote current heading and all headings in the
+subtree (from a Lisp program, pass `subtree' for WHICH); with prefix
+argument, promote just the current heading (from a Lisp program, pass
+nil for WHICH, or do not pass any argument)."