$re = '~(?(DEFINE)
(?<tagName>
[a-z][a-z\d]*+ (?=[>\s/])
)
(?<tagAttr>
(?>
[^>"\']++
| " [^"]*+ "
| \' [^\']*+ \'
)*+
)
)
< (li|/ul) /?+ (?=[>\s/]) ((?&tagAttr)) >
((?:
[^<]++
| < /?+ (?!(?:li|ul)(?=[>\s/])) (?&tagName) (?&tagAttr) > #any tag except <li> and <ul>
| < (?! /?+ (?&tagName) ) #not tag
)*)
(?= < (?:li|/ul) (?=[>\s/]) (?&tagAttr) ) #check for nested <li> and <ul>~sixuX';
$str = '<ul>
<li fhgfhfg ghgfhfghhfgh= ghghg="..." a = \'ghghg\'>dfdsfsd
<ul>
<li>111</li>
<li/>2222
<li>mmmmm</li>
</ul>
<li>dfdsfdsfsdf <b class="..."><br/>fgdfgd<i></b><!-- dfdf--><li>
<li>
<li>dsfsdfsdfdsf
</ul>
';
$subst = "<$3$4>$5</LI>\r";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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