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The Template for a Definition
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  The `@deffn' command is used for definitions of entities that
resemble functions.  To write a definition using the `@deffn' command,
write the `@deffn' command at the beginning of a line and follow it on
the same line by the category of the entity, the name of the entity
itself, and its arguments (if any).  Then write the body of the
definition on succeeding lines.  (You may embed examples in the body.)
Finally, end the definition with an `@end deffn' command written on a
line of its own.  (The other definition commands follow the same
format.)

  The template for a definition looks like this:

     @deffn CATEGORY NAME ARGUMENTS...
     BODY-OF-DEFINITION
     @end deffn

For example,

     @deffn Command forward-word count
     This command moves point forward @var{count} words
     (or backward if @var{count} is negative). ...
     @end deffn

produces

      - Command: forward-word count
          This function moves point forward COUNT words (or backward if
          COUNT is negative). ...

  Capitalize the category name like a title.  If the name of the
category contains spaces, as in the phrase `Interactive Command', write
braces around it.  For example:

     @deffn {Interactive Command} isearch-forward
     ...
     @end deffn

Otherwise, the second word will be mistaken for the name of the entity.

  Some of the definition commands are more general than others.  The
`@deffn' command, for example, is the general definition command for
functions and the like--for entities that may take arguments.  When you
use this command, you specify the category to which the entity belongs.
The `@deffn' command possesses three predefined, specialized
variations, `@defun', `@defmac', and `@defspec', that specify the
category for you: "Function", "Macro", and "Special Form" respectively.
(In Lisp, a special form is an entity much like a function.)  The
`@defvr' command also is accompanied by several predefined, specialized
variations for describing particular kinds of variables.

  The template for a specialized definition, such as `@defun', is
similar to the template for a generalized definition, except that you
do not need to specify the category:

     @defun NAME ARGUMENTS...
     BODY-OF-DEFINITION
     @end defun

Thus,

     @defun buffer-end flag
     This function returns @code{(point-min)} if @var{flag}
     is less than 1, @code{(point-max)} otherwise.
     ...
     @end defun

produces

      - Function: buffer-end flag
          This function returns `(point-min)' if FLAG is less than 1,
          `(point-max)' otherwise.  ...

Note: Sample Function Definition, for a
more detailed example of a function definition, including the use of
`@example' inside the definition.

  The other specialized commands work like `@defun'.

  Note that, due to implementation difficulties, macros are not expanded
in `@deffn' and all the other definition commands.