prm (PRoperty Modifier):

A field in piece table entries that records how the properties of text within a piece were changed to reflect user formatting operations. The prm usually contains an index to a grpprl which records the user's formatting changes as a group of sprms. If the user has made only a small change to formatting that can be expressed as a single 2 or 1-byte sprm, that sprm is stored within the prm.