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ext/pcre: document variable-length lookbehind and longer subpattern names (PHP 8.4) #5739

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ext/pcre: document variable-length lookbehind and longer subpattern names (PHP 8.4) #5739

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12 changes: 12 additions & 0 deletions reference/pcre/pattern.syntax.xml
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Expand Up @@ -1510,6 +1510,10 @@
also by name. There are two alternative syntaxes
<literal>(?&lt;name&gt;pattern)</literal> and <literal>(?'name'pattern)</literal>.
</para>
<simpara>
As of PHP 8.4.0, which bundles PCRE2 10.44, the maximum length of a
subpattern name is 128 characters; prior to PHP 8.4.0 it was 32 characters.

@jordikroon jordikroon Aug 13, 2026

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Suggested change
subpattern name is 128 characters; prior to PHP 8.4.0 it was 32 characters.
subpattern name is 128 characters; previously it was 32 characters.

</simpara>

<para>
Sometimes it is necessary to have multiple matching, but alternating
Expand Down Expand Up @@ -1915,6 +1919,14 @@
at the ends of strings; an example is given at the end
of the section on once-only subpatterns.
</para>
<simpara>
The fixed-length restriction described above applies prior to PHP 8.4.0.

@jordikroon jordikroon Aug 13, 2026

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We shouldn't mention that the behavior described above applies to older versions. Instead, we should move the older behaviour below and state that the current description applies to PHP 8.4.0 and later. The documentation should reflect the latest version by default, whereas behaviour from older versions should be documented separately as historical information.

As of PHP 8.4.0, which bundles PCRE2 10.44, a lookbehind assertion may match
strings of variable length: alternatives of differing lengths (such as
<literal>(?&lt;!dogs?|cats?)</literal>) and top-level branches that can match
more than one length (such as <literal>(?&lt;=ab(c|de))</literal>) are now
permitted, up to an implementation-defined maximum length.
</simpara>
<para>
Several assertions (of any sort) may occur in succession.
For example,
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