goto-address-url-regexp

goto-address-url-regexp is a variable defined in `goto-addr.el'.
Its value is

"\\<\\(aaa://\\|about:\\|acap://\\|apt:\\|bzr://\\|bzr+ssh://\\|attachment:/\\|chrome://\\|cid:\\|content://\\|crid://\\|cvs://\\|dav:\\|dict://\\|doi:\\|dns:\\|dtn:\\|feed:\\|file:/\\|finger://\\|fish://\\|ftp://\\|geo:\\|git://\\|go:\\|gopher://\\|h323:\\|http://\\|https://\\|im:\\|imap://\\|info:\\|ipp:\\|irc://\\|irc6://\\|ircs://\\|iris.beep:\\|jar:\\|ldap://\\|ldaps://\\|mid:\\|mtqp://\\|mupdate://\\|news:\\|nfs://\\|nntp://\\|opaquelocktoken:\\|pop://\\|pres:\\|resource://\\|rmi://\\|rsync://\\|rtsp://\\|rtspu://\\|service:\\|sftp://\\|sip:\\|sips:\\|smb://\\|sms:\\|snmp://\\|soap.beep://\\|soap.beeps://\\|ssh://\\|svn://\\|svn+ssh://\\|tag:\\|tel:\\|telnet://\\|tftp://\\|tip://\\|tn3270://\\|udp://\\|urn:\\|uuid:\\|vemmi://\\|webcal://\\|xri://\\|xmlrpc.beep://\\|xmlrpc.beeps://\\|z39.50r://\\|z39.50s://\\|xmpp:\\|fax:\\|mms://\\|mmsh://\\|modem:\\|prospero:\\|snews:\\|wais://\\)[^]	\n \"'<>[^`{}]*[^]	\n \"'<>[^`{}.,;]+"

Documentation:
A regular expression probably matching a URL.