<?php
$str = "Loreum Ipsum Dolor Sit Amet <code>Some HTML Code like <h1>Head</h1></code>. Loreum Ipsum <code>Some Code</code> Dolor Sit Amet.";
'|(?s)(?<=<code>).*?(?=</code>)|',
function ($matches) {
},
$str
);
echo $str;
PD9waHAKCiRzdHIgPSAiTG9yZXVtIElwc3VtIERvbG9yIFNpdCBBbWV0IDxjb2RlPlNvbWUgSFRNTCBDb2RlIGxpa2UgPGgxPkhlYWQ8L2gxPjwvY29kZT4uIExvcmV1bSBJcHN1bSA8Y29kZT5Tb21lIENvZGU8L2NvZGU+IERvbG9yIFNpdCBBbWV0LiI7CiRzdHIgPSBwcmVnX3JlcGxhY2VfY2FsbGJhY2soCiAgICAnfCg/cykoPzw9PGNvZGU+KS4qPyg/PTwvY29kZT4pfCcsCiAgICBmdW5jdGlvbiAoJG1hdGNoZXMpIHsKICAgICAgICByZXR1cm4gc3RyX3JlcGxhY2UoJzwnLCAnJmx0OycsICRtYXRjaGVzWzBdKTsKICAgIH0sCiAgICAkc3RyCik7CmVjaG8gJHN0cjs=