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Update PREG_UNMATCHED_AS_NULL description for trailing groups #5272

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Update PREG_UNMATCHED_AS_NULL description for trailing groups #5272

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46c970b
Clarify PREG_UNMATCHED_AS_NULL behavior for trailing groups
lacatoire Feb 5, 2026
b7a5ddd
Document PHP 7.4.0 change for trailing unmatched groups
lacatoire May 18, 2026
80b0ee0
pcre: use simpara for PREG_UNMATCHED_AS_NULL description (style guide)
lacatoire May 23, 2026
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6 changes: 4 additions & 2 deletions reference/pcre/constants.xml
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Original file line number Diff line number Diff line change
Expand Up @@ -94,8 +94,10 @@
<entry>
This flag tells <function>preg_match</function> and
<function>preg_match_all</function> to include unmatched subpatterns in
<varname>$matches</varname> as &null; values. Without this flag, unmatched
subpatterns are reported as empty strings, as if they were empty matches.
<varname>$matches</varname> as &null; values, including trailing
unmatched subpatterns. Without this flag, non-trailing unmatched
subpatterns are reported as empty strings, while trailing unmatched
subpatterns are omitted from the results entirely.
Setting this flag allows to distinguish between these two cases.
</entry>
<entry>7.2.0</entry>
Expand Down
20 changes: 16 additions & 4 deletions reference/pcre/functions/preg-match-all.xml
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Expand Up @@ -242,10 +242,14 @@ Array
<varlistentry>
<term><constant>PREG_UNMATCHED_AS_NULL</constant></term>
<listitem>
<para>
If this flag is passed, unmatched subpatterns are reported as &null;;
otherwise they are reported as an empty <type>string</type>.
</para>
<simpara>
If this flag is passed, unmatched subpatterns are reported as &null;
and are always included in the results (including trailing ones).
Without this flag, unmatched subpatterns that are followed by a
matched subpattern are reported as an empty <type>string</type>,
while trailing unmatched subpatterns are omitted from the results
entirely.
</simpara>
</listitem>
</varlistentry>
</variablelist>
Expand Down Expand Up @@ -301,6 +305,14 @@ Array
</row>
</thead>
<tbody>
<row>
<entry>7.4.0</entry>
<entry>
When the <constant>PREG_UNMATCHED_AS_NULL</constant> flag is used,
trailing unmatched capturing groups are now also included in the
result with the value &null;. Previously, they were omitted.
</entry>
</row>
<row>
<entry>7.2.0</entry>
<entry>
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38 changes: 36 additions & 2 deletions reference/pcre/functions/preg-match.xml
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Expand Up @@ -119,8 +119,12 @@ Array
<term><constant>PREG_UNMATCHED_AS_NULL</constant></term>
<listitem>
<para>
If this flag is passed, unmatched subpatterns are reported as &null;;
otherwise they are reported as an empty <type>string</type>.
If this flag is passed, unmatched subpatterns are reported as &null;
and are always included in the results (including trailing ones).
Without this flag, unmatched subpatterns that are followed by a
matched subpattern are reported as an empty <type>string</type>,
while trailing unmatched subpatterns are omitted from the results
entirely.
<informalexample>
<programlisting role="php">
<![CDATA[
Expand All @@ -129,6 +133,12 @@ preg_match('/(a)(b)*(c)/', 'ac', $matches);
var_dump($matches);
preg_match('/(a)(b)*(c)/', 'ac', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);

// Trailing unmatched subpatterns:
preg_match('/(a)(b)?(c)?/', 'a', $matches);
var_dump($matches);
preg_match('/(a)(b)?(c)?/', 'a', $matches, PREG_UNMATCHED_AS_NULL);
var_dump($matches);
?>
]]>
</programlisting>
Expand All @@ -155,6 +165,22 @@ array(4) {
[3]=>
string(1) "c"
}
array(2) {
[0]=>
string(1) "a"
[1]=>
string(1) "a"
}
array(4) {
[0]=>
string(1) "a"
[1]=>
string(1) "a"
[2]=>
NULL
[3]=>
NULL
}
]]>
</screen>
</informalexample>
Expand Down Expand Up @@ -270,6 +296,14 @@ Array
</row>
</thead>
<tbody>
<row>
<entry>7.4.0</entry>
<entry>
When the <constant>PREG_UNMATCHED_AS_NULL</constant> flag is used,
trailing unmatched capturing groups are now also included in the
result with the value &null;. Previously, they were omitted.
</entry>
</row>
<row>
<entry>7.2.0</entry>
<entry>
Expand Down