When using the extended [url=] BBCode to also use custom content for the link it is not possible to have linebreaks in it. The following usages will never validate:

[url=http://www.phpbb.com]Check out

phpBB 3.0.8![/url]

[url=http://www.phpbb.com][img]http://www.phpbb.com/theme/images/logo_phpbb.png[/img]

Check out phpBB![/url]

This is because in /includes/message_parser.php, function bbcode_init() we have:

		$this->bbcodes = array(

...

			'url'			=> array('bbcode_id' => 3,	'regexp' => array('#\[url(=(.*))?\](.*)\[/url\]#iUe' => "\$this->validate_url('\$2', '\$3')")),

...whereas the match pattern misses linebreaks.

I have two possible workarounds:

1. adding the s modifier (but this will in first place also allow URLs with linebreaks):

   'url' => array('bbcode_id' => 3, 'regexp' => array('#\[url(=(.*))?\](.*)\[/url\]#isUe' => "\$this->validate_url('\$2', '\$3')")),

2. or indirectly allowing linebreaks by not allowing a character which should never occur (NUL):

   'url' => array('bbcode_id' => 3, 'regexp' => array('#\[url(=(.*))?\]([^\x00]*)\[/url\]#iUe' => "\$this->validate_url('\$2', '\$3')")),