2C-mode is a compiled Lisp function in `two-column.el'.

(2C-mode OTHER)

Minor mode for independently editing two columns.
This is set up for two associated buffers by the three commands bound
to C-x 6 2 , C-x 6 b and C-x 6 s.
Turning on two-column mode calls the value of the variable `2C-mode-hook',
if that value is non-nil.

These buffers can be edited separately, for example with `fill-paragraph'.
If you want to disable parallel scrolling temporarily, use M-x 2C-toggle-autoscroll .

If you include long lines that span both columns (e.g., source
code), they should be in what will be the first column, with the
associated buffer having empty lines next to them.

Potential uses are writing bilingual texts, or editing the comments of a
source code. See the file lisp/two-column.el for detailed examples.

You have the following commands at your disposal:

C-x 6 2 Rearrange screen with current buffer first
C-x 6 b Reassociate buffer after changing major mode
C-x {, C-x } Shrink, enlarge current column
M-x 2C-associated-buffer Switch to associated buffer at same point
M-x 2C-newline Insert newline(s) in both buffers at same point
M-x 2C-merge Merge both buffers
M-x 2C-dissociate Dissociate the two buffers

These keybindings can be customized in your init file by
`2C-mode-map', `2C-minor-mode-map' and by binding `2C-command' to
some prefix.

The appearance of the screen can be customized by the variables
`2C-window-width', `2C-beyond-fill-column', `2C-mode-line-format' and