(*ACCEPT) behavior when forward-matching and when backtracking

[rsFalse]

https://perldoc.perl.org/perlre#(*ACCEPT)-(*ACCEPT:arg)

Description
From documentation:

... causes the end of successful matching at the point at which the (*ACCEPT) pattern was encountered, regardless of whether there is actually more to match in the string.

... is not clear when it should be encountered: 1) on backtracking (like (*SKIP)), or 2) on forward-tracking like (*FAIL) aka (?!).

Steps to Reproduce
In simplest case a verb is encountered on forward-tracking (b haven't match):

perlbrew exec perl -wle ' "ab" =~ /(?:a(*ACCEPT))b/; print "[$&]" '
perl-5.38.2, 5.36.0, 5.32.0, 5.20.1, 5.14.3
[a]

In this example it could be either forward-tracking behavior (look-ahead isn't even reached), or backtracking (third match with b survives because of acception):

perlbrew exec perl -we ' print "[$-[0]:$&]" while ( "b" x 3 ) =~ m/(?:b(*ACCEPT))(?=b)/g; print "\n" '
perl-5.38.2, 5.36.0
==========
[0:b][1:b][2:b]

perl-5.32.0, 5.20.1
==========
[0:b][1:b][2:b]

Same example but with atomic ((?>...)):

perlbrew exec perl -we ' print "[$-[0]:$&]" while ( "b" x 3 ) =~ m/(?>b(*ACCEPT))(?=b)/g; print "\n" '
perl-5.38.2, 5.36.0
==========
[0:b][1:b]

perl-5.32.0, 5.20.1
==========
[0:b][1:b]

...it looks like on the third match attempt (*ACCEPT) was not encountered at forward-tracking (otherwise it would succeed), and after a failure on look-ahead, it couldn't finish matching attempt because an atomic group haven't let to backtrack into itself and encounter a verb.
...same output as with possessive {1}+, except perl-5.20.1 where it was a bug.

Same as in non-atomic example, but with quantifier {1} added. Should be the same. Differences are in older versions:

perlbrew exec perl -we ' print "[$-[0]:$&]" while ( "b" x 3 ) =~ m/(?:b(*ACCEPT)){1}(?=b)/g; print "\n" '
perl-5.38.2, 5.36.0
==========
[0:b][1:b][2:b]

perl-5.32.0, 5.20.1
==========
[0:b][1:b]

Same but with quantifier +. Both (?>...) (not shown) and (?:...) outputs the same:

perlbrew exec perl -we ' print "[$-[0]:$&]" while ( "b" x 3 ) =~ m/(?:b(*ACCEPT))+(?=b)/g; print "\n" '
perl-5.38.2, 5.36.0
==========
[0:b][1:b][2:b]

perl-5.32.0, 5.20.1
==========
[0:bb]

...in the latest versions a verb seems to be encountered on forward-tracking. Otherwise it should have matched [0:bbb] IMO, which is somehow similar to the outputs of earlier versions.

Expected behavior
Not clearly defined when a verb should be encountered.

[florian-pe]

It acts when "forward-matching", but there is an implementation issue concerning backtracking control.

You can match on backtracking with something like / ... (*PRUNE) (?: | (*ACCEPT)) ... /.

edit: (*PRUNE) is irrelevant however.