$re = '/\,id::([^}]*?)::]]><\/string2>/m';
$str = '[...]
<item1>
<string1>sometext</string1>
<string2><![data[text1, text2,id::aR0sddcsb3NoaQ=::]]></string2>
<string3>sometext</string3>
<item1>
<item2>
<string1>sometext</string1>
<string2><![data[text1, text2,id::furmdjd73ks=::]]></string2>
<string3>sometext</string3>
<item2>
<item3>
<string1>sometext</string1>
<string2><![data[text1, text2,id::h6eefvndjd73ks=::]]></string2>
<string3>sometext</string3>
<item3>
[...]';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php