php checks whether username complies with regulations

http://blog.ddian.cn/?post=869

/**
 * Check whether the username meets the regulations (more than two characters, only Chinese, letters, numbers, and underscores)
 *
 * @param STRING $username The username to be checked
 * @return TRUE or FALSE
*/
function is_username($username) {
 $strlen = strlen($username);
 if(!preg_match("/^[a-zA- Z0-9_x7f-xff][a-zA-Z0-9_x7f-xff]+$/", $username)){
 return false;
 } elseif ( 20  return false;
 }
 return true;
}


//The following test
$str = 'abc';
if(is_username($str)) {
 echo $str.'match';
}else {
 echo $str.'does not match';
}
echo '';

$str = 'Chinese';
if(is_username($str)) {
 echo $str.'matches';
}else {
 echo $str.'does not match';
}
echo '';

$str = '12126_($@';
if(is_username($str)) {
 echo $str.'match';
}else {
 echo $str.'not match';
}

?>