gnus: Summary Highlighting

 
 3.1.4 Summary Highlighting
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 ‘gnus-visual-mark-article-hook’
      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’.
 
 ‘gnus-summary-update-hook’
      This hook is called when a summary line is changed.  It is not run
      if ‘gnus-visual’ is ‘nil’.
 
 ‘gnus-summary-selected-face’
      This is the face (or “font” as some people call it) used to
      highlight the current article in the summary buffer.
 
 ‘gnus-summary-highlight’
      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.