> >     (defgroup highlight-80+ nil
  > >       "Highlight characters beyond column 80."
  > >       :group 'faces)
  > >

  > >     (defcustom highlight-80+-columns 80
  > >       "*Number of columns to allow in lines."
  > >       :group 'highlight-80+
  > >       :type 'integer)

  > >
  > > Perhaps this should be a standard feature
  > > so that this variable could have a shorter and more natural name.
  > >
  >
  >
  > Well, whitespace.el has a similar feature:
  >
  >
  > ;; Thanks to nschum (EmacsWiki) for the idea about highlight "long"
  > ;; lines tail.  See EightyColumnRule (EmacsWiki).

Can you please document this at least in etc/NEWS?  Otherwise it's very
hard to guess that such a feature would be found in whitespace.el ...

You're right! I had not much time to do it, but I'll put the whitespace.el main features in etc/NEWS.

  > (defcustom whitespace-line-column 80
  >  "*Specify column beyond which the line is highlighted.
  >
  > Used when `whitespace-style' includes `lines' or `lines-tail'."
  >  :type '(integer :tag "Line Length")
  >  :group 'whitespace)