gnus-button-url-regexp

gnus-button-url-regexp is a variable defined in `gnus-art.el'.
Its value is

"\\b\\(\\(www\\.\\|\\(s?https?\\|ftp\\|file\\|gopher\\|nntp\\|news\\|telnet\\|wais\\|mailto\\|info\\):\\)\\(//[-a-z0-9_.]+:[0-9]*\\)?\\(?:[-a-z0-9_=#$@~%&*+\\/[:word:]!?:;.,]+([-a-z0-9_=#$@~%&*+\\/[:word:]!?:;.,]+[-a-z0-9_=#$@~%&*+\\/[:word:]]*)\\(?:[-a-z0-9_=#$@~%&*+\\/[:word:]!?:;.,]+[-a-z0-9_=#$@~%&*+\\/[:word:]]\\)?\\|[-a-z0-9_=#$@~%&*+\\/[:word:]!?:;.,]+[-a-z0-9_=#$@~%&*+\\/[:word:]]\\)\\)"

Documentation:
Regular expression that matches URLs.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.4 of Emacs.