Ifaceshift$ ()

   Synopsis:
      Removes and returns the first item of additional data provided by the
         interface when it fired

   Notes:
      The interface notification list contains all the notifications received,
         and not yet processed, as the result of an earlier SETTRIG, SETALIAS,
         SETMACRO, SETTIMER or SETHOOK statement.
      This function operates on the current notification (usually the first one;
         see the help for SKIPIFACE).

      The Ifacetext$ () function returns whatever caused the interface to fire.
         Some interfaces provide additional data when they fire, but some do
         not. The help for Ifacedefined () contains more information about this.
      This function removes the first remaining item of additional data, and
         returns it. You can call Ifaceshift$ () repeatedly until there is no
         more additional data to remove.
      When there is no more additional data to remove, or if the notification
         list itself is empty, returns an empty string.
