+;; the default value was copied from gnus-button-url-regexp
+(defcustom riece-url-regexp
+ (concat
+ "\\b\\(\\(www\\.\\|\\(s?https?\\|ftp\\|file\\|gopher\\|"
+ "nntp\\|news\\|telnet\\|wais\\|mailto\\|info\\):\\)"
+ "\\(//[-a-z0-9_.]+:[0-9]*\\)?"
+ (if (string-match "[[:digit:]]" "1") ;; Support POSIX?
+ (let ((chars "-a-z0-9_=#$@~%&*+\\/[:word:]")
+ (punct "!?:;.,"))
+ (concat
+ "\\(?:"
+ ;; Match paired parentheses, e.g. in Wikipedia URLs:
+ ;; http://thread.gmane.org/47B4E3B2.3050402@gmail.com
+ "[" chars punct "]+" "(" "[" chars punct "]+" "[" chars "]*)" "[" chars "]*"
+ "\\|"
+ "[" chars punct "]+" "[" chars "]"
+ "\\)"))
+ (concat ;; XEmacs 21.4 doesn't support POSIX.
+ "\\([-a-z0-9_=!?#$@~%&*+\\/:;.,]\\|\\w\\)+"
+ "\\([-a-z0-9_=#$@~%&*+\\/]\\|\\w\\)"))
+ "\\)")