How do I match any character across multiple lines in a regular expression?

([\s\S]*)<FooBar>

The dot matches all except newlines (\r\n). So use \s\S, which will match ALL characters.

"." normally doesn't match line-breaks. Most regex engines allows you to add the S-flag (also called DOTALL and SINGLELINE) to make "." also match newlines. If that fails, you could do something like [\S\s].