found (what I believe to be) a minor error in the documentation (online and pdf)

pdf documentation version 1-1: pages 222-223

listing 13-42:
---
\# schema.yml
\# ...
User:
columns:
username:
type: string(255)
regexp: '/[a-zA-Z0-9]/'
\# ...

listing 13-43:
// test.php
// ...
$user = new User();
$user->username = '[jwage';
if ( ! $user->isValid()) {
echo 'User is invalid because the username contains a [ character';
}

is this correct?
or would the regex need to be: "/^[a-zA-Z0-9]+$/"

..seems that since the username "[jwage" contains at least one character in the set, it should match against the regex

..I probably shouldn't even ask.. being brand new to Doctrine. But it feels like a small documentation mistake when reading it. Thought I'd pass it along to someone who knows better. Thanks.