#### A.1.13 Documentation and Test of Oct-Files

The documentation of an oct-file is the fourth string parameter of the `DEFUN_DLD` macro. This string can be formatted in the same manner as the help strings for user functions (Documentation Tips), however there are some issue that are particular to the formatting of help strings within oct-files.

The major issue is that the help string will typically be longer than a single line of text, and so the formatting of long help strings need to be taken into account. There are several manners in which to treat this issue, but the most common is illustrated in the following example,

         DEFUN_DLD (do_what_i_want, args, nargout,
           "-*- texinfo -*-\n\
         @deftypefn {Function File} {} do_what_i_say (@var{n})\n\
         A function that does what the user actually wants rather\n\
         than what they requested.\n\
         @end deftypefn")
         {
         ...
         }

where, as can be seen, end line of text within the help string is terminated by `\n\` which is an embedded new-line in the string together with a C++ string continuation character. Note that the final `\` must be the last character on the line.

Octave also includes the ability to embed the test and demonstration code for a function within the code itself (Test and Demo Functions). This can be used from within oct-files (or in fact any file) with certain provisos. Firstly, the test and demo functions of Octave look for a `%!` as the first characters on a new-line to identify test and demonstration code. This is equally a requirement for oct-files. Furthermore the test and demonstration code must be included in a comment block of the compiled code to avoid it being interpreted by the compiler. Finally, the Octave test and demonstration code must have access to the source code of the oct-file and not just the compiled code as the tests are stripped from the compiled code. An example in an oct-file might be

         /*

         %!error (sin())
         %!error (sin(1,1))
         %!assert (sin([1,2]),[sin(1),sin(2)])

         */