Good day!
There are some kinds of problems that exist with max_lookbehind:
- bugs
- performance issues
- brings excessive work to user
Now I report only about potential bugs.
Here is pcre2test output:
PCRE2 version 10.34-RC1 2019-04-22
/(?<=(?=(?<=.)).)/info,allusedtext
Capture group count = 0
Max lookbehind = 1
May match empty string
Subject length lower bound = 0
ab
0: ab
<<
/(?<=\A.)/info,allusedtext
Capture group count = 0
Max lookbehind = 1
May match empty string
Subject length lower bound = 0
ab
0: a
<
/(?<=\G.)/info,allusedtext
Capture group count = 0
Max lookbehind = 1
May match empty string
Subject length lower bound = 0
ab
0: a
<
In all 3 cases we see that Max lookbehind = 1
but it seems it must be 2.
\A and \G may be considered as (?<!.) in dotall mode
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