one of the documented procedures in this installation of the ACS
link_urls   str
What it does:
Replace what appear to be URLs with links.
Defined in: /web/philip/tcl/chat-defs.tcl

Source code:

    # URL courtesy of Zach Beane, somewhat modified. If you can do better,
    # let me know
    set url_re {(http|ftp)://[-A-Za-z0-9]+(\.[-A-Za-z0-9]+)+(:[0-9]+)?(/[-^A-Za-z0-9_~\#/]*)?([./][-^A-Za-z0-9_~\#?=%+/]+)*}
    regsub -all $url_re $str {<a target=newwindow href="\0">\0</a>} str

    # Try to get "" linked properly (without re-linking
    # any of the URLs we just linked).

    set url_re_no_http {([^/])(www\.[-A-Za-z0-9]+(\.[-A-Za-z0-9]+)+(:[0-9]+)?(/[-^A-Za-z0-9_~\#/]*)?([./][-^A-Za-z0-9_~\#?=%+/]+)*)}
    regsub -all $url_re_no_http $str {\1<a target=newwindow href="http://\2">\2</a>} str
    return $str