gnus-button-man-handler

gnus-button-man-handler is a variable defined in `gnus-art.el'.
Its value is

manual-entry

Documentation:
Function to use for displaying man pages.
The function must take at least one argument with a string naming the
man page.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.