Editing Help text style guide

Functions should have help text so that people know how to use it.

= Guidelines =
== First sentence ==
The first sentence of help text should start with a statement that is like a command. For example, the first sentence of {{Codeline|hist}}:
<pre>
Produce histogram counts or plots.         # good
Produces histogram counts or plots.        # bad
hist produces histogram counts or plots.   # bad
</pre>

== Manual reference ==
When submitting a function to Octave, a tag for the docstring should be added to some appropriate place in one of the manual's .txi source files (they are all in {{Path|doc/interpreter/}}). Find the most appropriate section in the manual and add the following with the related functions:
{{Code|adding tag for function help text in Octave's manual|<pre>
+@DOCSTRING(function_name)
</pre>}}

If appropriate, also write some text about the function on the manual for better inclusion into the manual.

== Sentence spacing ==
The typographical convention in Octave is to use two full spaces after a period that ends a sentence. For example:
<pre>
there is no correct for sentence spacing.  But we need a convention # good
there is no correct for sentence spacing. But we need a convention  # bad
</pre>

= TexInfo =
This is the preferred format for help text. There is also a comprehensive [http://www.gnu.org/software/texinfo/manual/texinfo/html_node/index.html TexInfo manual].

== Octave specific macros ==
=== seealso ===
Do not use this macro empty as it will create problems with the {{forge|generate_html}} package.
=== deftypefn ===
This environment will enclose the function help text. It takes as argument the type of function. Typical values are
* Function File -- for functions in .m files
* Loadable Function -- for functions in .oct files
* Accessor method
* Class property

Besides this environment there is also the alternative {{Codeline|deftypenx}} for alternative forms. Typically these are mentioned at the top of the help text, right after the {{Codeline|deftypen}} although this is not really necessary. Cases where it's acceptable to have them on other sections would be methods on the help text of a class constructor, since they will not always be on a separate file.

== Formatting ==

=== Formulas ===
Do not use the example environment to insert formulas, consider using {{Codeline|@verbatim}} instead. 

{{Code||<pre>
@verbatim
           E[Z(i,k) ]
IRL(k) =  ------------
              V(i)
@end verbatim
</pre>}}

However, this will never print as a nice looking mathematical formula that TeX is known for. It is possible to have Tex formulas but then they won't be displayed on HTML or Info (Octave help) so the following can be done:

{{Code||<pre>
@tex
\def\frac#1#2{{\begingroup#1\endgroup\over#2}}
$$ IRL(k) = \frac{E[Z(i,k)]}{V(i)} $$
@end tex
@ifnottex
@verbatim
           E[Z(i,k) ]
IRL(k) =  ------------
              V(i)
@end verbatim
@end ifnottex
</pre>}}

=== Plain-tex missing macros ===
When compared to LaTeX, plain TeX is missing some very useful macros for including mathematical notation. The following is a list of their definitions which can be added on a as needed basis:

* frac
<pre>\def\frac#1#2{{\begingroup#1\endgroup\over#2}}</pre>

== Special inserts ==
=== Escape characters ===
To escape characters in TexInfo, use the character {{Codeline|@}}. Only the characters '''@''', '''{''' and '''}''' need to be escaped.

* {{Codeline|<nowiki>@@</nowiki>}} stands for a single '''@''' (do not put braces after an {{Codeline|<nowiki>@@</nowiki>}} command)
* {{Codeline|<nowiki>@{</nowiki>}} stands for a single '''{'''
* {{Codeline|<nowiki>@}</nowiki>}} stands for a single '''}'''

In certain contexts (such as {{Codeline|@acronym}} or {{Codeline|@xref}}), commas may need to be escaped. In such situations, use {{Codeline|<nowiki>@comma{}</nowiki>}}.

=== Ellipsis (...) ===
Ellipsis are frequently used in octave help text, specially when defining a function API. Use the {{Codeline|<nowiki>@dots{}</nowiki>}} rather than three dots.

{{Code||<pre>
@deftypefn {Function File} {} imhist (@var{I})
@deftypefnx {Function File} {[@var{counts}, @var{x}] =} imhist (@dots{})
</pre>}}

=== Matlab ===
Sometimes it is need to mention matlab in the help text. For example, to mention that a weird behavior needs to be kept for matlab compatibility. In such case, small caps should be used. For example, the following is used in the {{Codeline|length}} help text:

{{Code||<pre>
For matrix objects, the length is the number of rows or columns, whichever is
greater (this odd definition is used for compatibility with @sc{matlab}).
</pre>}}