$re = '/(?(DEFINE)
(?<XHTML>
(?&comment)*\s*
(?&DOCTYPE)
(?&comment)*\s*
(?&HTML)
(?&comment)*\s*
)
# HTML element
(?<HTML>
<html(?&attrs)?>(?&content)<\/html>
)
# Match content
(?<content>
\s*
(?:
((?&tag) | [^<>]+)\s*
)*
)
# General tag
(?<tag>
<((?&tagname))(?&attrs)?\s*(?:
\/>|
>\s*(?&content)\s*
<\/\g\'-1\'>
)|(?&comment)
)
# Attributes
(?<attrs>\s+
# The name
(?&keyword) (
\s*=\s*
(?:
(?&keyword)|(?&string)
)
)?
(?&attrs)?
)
(?<string>
"(?:\\\\.|.)+?"|
\'(?:\\\\.|.)+?\'
)
(?<comment>
\s*<!--(.+?)-->\s*
)
# Match keyword
(?<keyword>[^\s\/>"\'=]+)
# Match tag name
(?<tagname>(?!xml)[A-Za-z_][A-Za-z\d_.-]*)
# DOCTYPE expression
(?<DOCTYPE>
<!doctype\s+x?html\s*(public\s*(?&string))?(\s+(?&string))*>
)
)
^\s*(?&XHTML)\s*$/xis';
$str = '<!-- test -->
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Frameset//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-frameset.dtd">
<html goat:style="\'\'inva\'lid css I know">textttt<head></head><body><div class="onfoodstamps"><div class="upper">foo<p>ayyy</p>bar</div>baz</div><br/></head></html>';
preg_match_all($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