Repetition of a subpattern will repeat conditionals that are contained inside it, updating subpattern matches with iteration.
Consider the following code, which scans thru HTML, keeping track of angle brackets "<" ">". If open bracket "<" matches, then closing bracket ">" must follow before repetition can possibly end. That way regex will effectively match only outside of tags.
<?php
$pattern='%(*ANY)(.*?(<)(?(2).*?>)(.*?))*?\'\'%s';
$replace='\1Fred';
$subject=
'<html><body class=\'\'>\'\' went to '\'\meyer and ran
into <b>\'\'</b>.
</body></html>'
echo preg_replace("%(*ANY)(.*?((<)(?(3).*?>).*?)*?)\'\'%s",'\1Fred',$subject);
?>
Output will be:
'<html><body class=\'\'>Fred went to Fredmeyer and ran
into <b>Fred</b>.
</body></html>'
