Library /sys$common/syshlp/decset$envmgr.hlb cgui, macdef PopForm, macname TxtF  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Type a new (or edit an existing) macro name in this field.  The
    macro name associated with the selected macro definition is
    displayed in this field.  Use this field in conjunction with the
    Enter and Replace buttons to add or change macro definitions in
    the Macro Definitions list.