Outline mode is a major mode derived from Text mode, which is
specialized for editing outlines. It provides commands to navigate
between entries in the outline structure, and commands to make parts
of a buffer temporarily invisible, so that the outline structure may
be more easily viewed. Type M-x outline-mode to switch to
Outline mode. Entering Outline mode runs the hook
text-mode-hook followed by the hook
When you use an Outline mode command to make a line invisible (see Outline Visibility), the line disappears from the screen. An ellipsis (three periods in a row) is displayed at the end of the previous visible line, to indicate the hidden text. Multiple consecutive invisible lines produce just one ellipsis.
Editing commands that operate on lines, such as C-n and C-p, treat the text of the invisible line as part of the previous visible line. Killing the ellipsis at the end of a visible line really kills all the following invisible text associated with the ellipsis.
Outline minor mode is a buffer-local minor mode which provides the same commands as the major mode, Outline mode, but can be used in conjunction with other major modes. You can type M-x outline-minor-mode to toggle Outline minor mode in the current buffer, or use a file-local variable setting to enable it in a specific file (see File Variables).
The major mode, Outline mode, provides special key bindings on the
C-c prefix. Outline minor mode provides similar bindings with
C-c @ as the prefix; this is to reduce the conflicts with the
major mode's special commands. (The variable
outline-minor-mode-prefix controls the prefix used.)