$re = '/<+[^\s<](?:[^<>]*[^\s<>])?>+/m';
$str = 'a <a bc> de
a <<a bc>> de
a <a bc> >de
a <<a bc> de
a <>a bc> de
a < a bc> de
a <a bc > de
a <<a bc >> de
a <a bc >> de';
preg_match_all($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