ssget visibility behaviour: _C/_W vs _F/_CP/_WP

Roumen
Roumen
in LISP

While working through some performance ("Turbo") testing of AutoLISP routines, I noticed something that I don't recall seeing explicitly documented.

It is well known that:

(ssget "_C" p1 p2 filter)

(ssget "_W" p1 p2 filter)

fail when the selection window is completely outside the current view.

But my testing suggests:

(ssget "_F" pts filter)

(ssget "_CP" pts filter)

(ssget "_WP" pts filter)

continue to work correctly even when the relevant geometry is completely off-screen.

In other words, the following appears to be true:

_C viewport dependent

_W viewport dependent

_F viewport independent

_CP viewport independent

_WP viewport independent

This came up while removing hundreds of internal zoom operations from older routines. After removing all (zoom) calls:

(ssget "_F" ...)

continued to work perfectly on geometry outside the current view.

Questions:

  1. Can others reproduce this in recent BricsCAD versions?
  2. Is this behaviour documented anywhere?
  3. Is this inherited from AutoCAD, or is it specific to BricsCAD's implementation?
  4. Does BricsCAD internally treat _F, _CP, and _WP differently from _C and _W?

I'm not asking about _C/_W requiring visibility (that part seems well known). I'm specifically interested in whether anyone has previously noted that _F/_CP/_WP appear not to share that limitation.