IFACEPOP$ ()

   Synopsis:
      Returns the last substring stored in the current interface notification

   Notes:
      The interface notification list contains all the notifications received,
         and not yet processed, as the result of an earlier SETTRIG statement.
      The substring (backreference) is removed from the notification, so you can
         call IFACEPOP$() repeatedly until there are no more substrings to
         remove. When there are no more substrings to remove, IFACEPOP$ returns
         an empty string.
      If there is no current notification, returns an empty string.
