-The meaningful PARMs depend on the kind of frame.
-Undefined PARMs are ignored, but stored in the frame's parameter list
-so that `frame-parameters' will return them.
+Which PARMs are meaningful depends on the kind of frame.
+The meaningful parameters are acted upon, i.e. the frame is changed
+according to their new values, and are also stored in the frame's
+parameter list so that `frame-parameters' will return them.
+PARMs that are not meaningful are still stored in the frame's parameter
+list, but are otherwise ignored.