(form "50110" (size 51  6)
  (heading "TARGET FILE DEFINITION")
  (label (position  5  3) (text "Target File"))
  (field "target_file" (position 20  3) (display_length 26) (input allowed)
    (translate lower) (null disallowed) (max_length 26)
    (file (extension trim "*.trg"))
    )
  (default_buttons)
)