What can happen if i use a loose URL chars restriction?

[eluser]Rick Jolly[/eluser]
You just need to be concerned if you are echoing anything from your url. For example, you wouldn't want to print this to the browser: "controller/method/<scribt>alert('may I steal your cookie?')</scribt>". As long as you run the uri or it's segments through htmlspecialchars(), then you won't have a problem.

Kohana has actually done away with the allowed url characters restriction.