Emacs background color limited to region

I was wondering how I could set the background color for a given region of the emacs frame.

The programming standard I'm following specifies max line width of 80 chars, which sometimes is ignored for convenience and readability. Now, say the frame is of some 开发者_如何学Gowidth greater than 80 chars, it would be very nice if this outside region could have a different background color.

If anyone could assist, I'd be very grateful.

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Already done for you. Read:

• http://www.emacswiki.org/emacs/EightyColumnRule
• http://www.emacswiki.org/emacs/FillColumnIndicator
• http://www.emacswiki.org/emacs/ModeLinePosition
• http://www.emacswiki.org/emacs/FindLongLines

and follow links.