Description:
------------
see below test script and expected and observed behavior below.

Maybe this an issue at the level of regular expressions specifications. As I only use them in PHP, I don't know, so I report it here. Also, it's so evidently flawed that maybe PHP could implement them correctly anyway while waiting for the specs to be fixed; not sure about that.

Test script:
---------------
<?php

$content = <<<'HERE'

First match: foo::"XYZ"
Second match: bar--<XYZ>

HERE;


$content=preg_replace_callback('#foo::"(?<sub>[^"]*)"|bar--<(?<sub>[^>]*)>#', 'testReplace', $content);

function testReplace($match) {
    
    print_r($match);
    return 'XXX';
}

Expected result:
----------------
Array
(
    [0] => foo::"XYZ"
    [sub] => XYZ
    [1] => XYZ
)
Array
(
    [0] => bar--<XYZ>
    [1] => 
    [sub] => XYZ
    [2] => XYZ
)


Actual result:
--------------
Warning: preg_replace_callback(): Compilation failed: two named subpatterns have the same name


Because the subgroups with the same name appear on two sides of a "|", there should be no conflict. At most one of the piped patterns (i.e. either side of the "|") can match, they are mutually exclusive, so there is no ambiguity possible and it should be a problem that a subgroup appear in both of them with the same name, as it can only be assigned once anyway.