Guide to LaTeX (4th Edition) (Tools and Techniques

\StopEventually{final text}
D.7. Managing code and documentation 469
where final text is to appear at the very end of the article; if only the
description part is printed, final text is printed immediately and the
documentation is ended.
The coding part
The coding part should normally contain the more specialized material
that is of no interest to the everyday user. The special commands that
may be used here are
\begin{macro}{\macro name} text and code \end{macro}
\begin{environment}{env name} text and code \end{environment}
both of which again insert a marginal note and make an entry in the index.
They also organize any \changes commands, as explained below.
The most important environment in the coding part is macrocode,
which prints its contents as in verbatim, optionally with a code line
number. The form of this environment is somewhat special:
\begin{macrocode}
lines of code
\end{macrocode}
The four spaces before the \end{macrocode} are obligatory; those before
the \begin are not necessary, but it is good practice to insert them for
symmetry. This environment also counts all the backslashes within it for
a checksum test, and makes an index entry for every command name that
it finds. So it is something more than a mere verbatim environment!
The coding part is brought to an end with
\Finale
which carries out the checksum test and prints the stored final text from
\StopEventually. There may actually be more text following it, which
is only printed when both description and coding parts are output.
Index of macros and record of changes
The doc package makes automatic entries into an index by means of
the two \Describexxx commands and the two environments presented
above. As well, all commands that appear in the coding are indexed.
However, the indexing is turned on only if one of
\CodelineIndex or \PageIndex
is given in the preamble. The first references the indexed commands to
the number of the code line where they appear, the second to the page