$re = '/(?=urce>)[\s\S]*?(?<=<\/datas)/';
$str = '<id>SomeID</id>
<datasource>C:/projects/my_project/my_file.jpg</datasource>
<title>My title can include / and other characters</title>
<abstract></abstract>';
preg_match_all($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