Description:
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Using the PCRE_EXTRA modifier as an internal option setting inside the pattern string now produces a warning:
"Warning: preg_match(): Compilation failed: unrecognized character after (? or (?- at offset 2"

I'm not really sure if this is intentional, as the RFC states:
"The current patch reverts the behavior to the meaning of 'X' how it was in PCRE"
https://wiki.php.net/rfc/pcre2-migration

If it indeed is intentional, then at least the documentation should be updated accordingly:
http://php.net/manual/en/regexp.reference.internal-options.php

Test script:
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preg_match('/(?X)/', '');