it can be used to check if a url is valid or not or to get urls from a text.

======
set blabla {http://www.ietf.org/rfc/rfc3986.txt}
if {[regexp -- {^(https?://[a-z0-9\-]+\.[a-z0-9\-\.]+(?:/|(?:/[a-zA-Z0-9!#\$%&'\*\+,\-\.:;=\?@\[\]_~]+)*)))$} $blabla match url]} {
        puts "$url is a valid url."
}
======


let's test it and post results here...

PS: don't work for ipv6 yet