This hook is run after selecting an article. It is meant to be used for highlighting the article in some way. It is not run if gnus-visual is nil.

This hook is called when a summary line is changed. It is not run if gnus-visual is nil.

This is the face (or font as some people call it) used to highlight the current article in the summary buffer.

Summary lines are highlighted according to this variable, which is a list where the elements are of the format (FORM . FACE). If you would, for instance, like ticked articles to be italic and high-scored articles to be bold, you could set this variable to something like

(((eq mark gnus-ticked-mark) . italic)
 ((> score default) . bold))

As you may have guessed, if FORM returns a non-nil value, FACE will be applied to the line.