$re = '/(<title>((?:(?!<\/title>).)*)<\/title>\s*<content>)((?:(?!<\/content>).)*)/';
$str = '<xml>
<item>
<title>Title 1</title>
<content>Text 1</content>
</item>
<item>
<title>Title 2</title>
<content>Text 2</content>
</item>
</xml>';
$subst = "$1$2 $3";
$result = preg_replace($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