$re = '/(\s*<[^>]+>\s*)+/m';
$str = '<h1>Heading</h1>
<br>
<br />
<a href="#">hyperlink</a>
<p></p>
<p>paragraph1</p>
<p>paragraph2</p>';
$subst = " ";
$result = preg_replace($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