BLIOVLOPS
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  Function : Get size of overlay pool memory.

  Syntax   : nlValue = BLIOVLOPS()

  Return   : Overlay Pool Operating Size in bytes

  This function returns the operating size of the overlay
  pool in bytes.

  This is set at link time using the BLINKER OVERLAY OPSIZE <size>
  command, or at run time using the /OOnn setting in the BLINKER
  environment variable. (see Chapter 6 BLINKER OVERLAY OPSIZE).

  The figure returned by this function represents the requested size of
  the overlay area at the time the program started running. This value
  will be the most recent of the value set at link time with the BLINKER
  OVERLAY OPSIZE nnn command and the /OOnnn setting of the BLINKER
  environment variable at runtime. The actual size of the area allocated
  may vary depending on the availability of EMS and UMBs and the settings
  of the appropriate BLINKER options. See the function BLIOVLSIZ() for
  details of the actual size allocated.

  Clipper Summer '87 DYNAMIC method note:

  When using the BLINKER OVERLAY DYNAMIC (the default) method of overlay
  allocation, this size is the maximum amount of memory which Blinker will
  allocate from Clipper for overlays. Once Blinker has used this much
  memory for overlays, it will discard unused overlays to free up space
  for the next overlay, rather than allocating more dynamic memory from
  Clipper to store the overlay.

  During execution the overlay manager may be forced to increase this
  value if overlays become heavily nested, since all active overlays must
  remain in memory with the DYNAMIC method. The new value will remain
  current until the program is ended unless a BLIOVLCLR() is executed. In
  this case the OPSIZE, and therefore the value returned by the
  BLIOVLOPS() function, will be reset to the value defined at start-up.

  Example  :
  *  Get the overlay pool operating size.
  *
  ? "The overlay pool operating size is "
  ?? BLIOVLOPS(), " bytes"