Format of Outlines
Outline mode assumes that the lines in the buffer are of two types:
heading lines and body lines. A heading line represents a
topic in the outline. Heading lines start with one or more stars; the
number of stars determines the depth of the heading in the outline
structure. Thus, a heading line with one star is a major topic; all the
heading lines with two stars between it and the next one-star heading
are its subtopics; and so on. Any line that is not a heading line is a
body line. Body lines belong with the preceding heading line. Here is
an example:
* Food
This is the body,
which says something about the topic of food.
** Delicious Food
This is the body of the second-level header.
** Distasteful Food
This could have
a body too, with
several lines.
*** Dormitory Food
* Shelter
Another first-level topic with its header line.
A heading line together with all following body lines is called
collectively an entry. A heading line together with all following
deeper heading lines and their body lines is called a subtree.
You can customize the criterion for distinguishing heading lines
by setting the variable outline-regexp. Any line whose
beginning has a match for this regexp is considered a heading line.
Matches that start within a line (not at the left margin) do not count.
The length of the matching text determines the level of the heading;
longer matches make a more deeply nested level. Thus, for example,
if a text formatter has commands @chapter, @section
and @subsection to divide the document into chapters and
sections, you could make those lines count as heading lines by
setting outline-regexp to "@chap\\|@\\(sub\\)*section".
Note the trick: the two words chapter and section are equally
long, but by defining the regexp to match only chap we ensure
that the length of the text matched on a chapter heading is shorter,
so that Outline mode will know that sections are contained in chapters.
This works as long as no other command starts with @chap.
You can change the rule for calculating the level of a heading line
by setting the variable outline-level. The value of
outline-level should be a function that takes no arguments and
returns the level of the current heading. Some major modes such as C,
Nroff, and Emacs Lisp mode set this variable and outline-regexp
in order to work with Outline minor mode.
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