Library /sys$common/syshlp/helplib.hlb  —  PASCAL  Input Output, General  OPEN  User Action
  The 'user_action' is the name of a user-written routine that VSI
  Pascal calls to open the file (instead of allowing VSI Pascal to
  open  the  file  with  the  OPEN  procedure).   You  can  use  a
  user-action  routine to open the file using environment-specific
  capabilities of the I/O system underlying HP Pascal.
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