column-enforce-mode
Highlight text that extends beyond a certain column.
This mode is meant to be a very lightweight, zero configuration, way to help enforce the 80 column rule. It can be configured for any N-column rule however.
What it looks like enforcing the 80 column rule:
Usage
Start it up interactively on the current buffer,
default startup: M-x: column-enforce-mode or by specific rule function M-x: 80-column-rule or with a prefix arg specifying the column limit C-u 90 M-x column-enforce-n
or tie it to a major mode:
(add-hook 'c-mode-hook 'column-enforce-mode)
tie it to all source code modes:
(add-hook 'prog-mode-hook 'column-enforce-mode)
or enable globally
(global-column-enforce-mode t)
Allowing long comments
By default column-enforce-mode will mark comments that exceed the limit. You can allow long comments in your code with:
(setq column-enforce-comments nil)
Customizing the column
(setq column-enforce-column <your desired column>)
Customizing the look
Customize `column-enforce-face’ to change the look of the mode