.dtx files).dtx, and will normally be ‘stripped’ before use with
LaTeX; an installation file (.ins) is normally provided,
to automate this process of removing comments for speed of loading.
To read the comments, you can run LaTeX on the
.dtx file to produce a nicely formatted version of the
documented code. Several
packages can be included in one .dtx file (they’re sorted
out by the .ins file), with conditional
sections, and there are facilities for indexes of macros, etc.
Anyone can write .dtx files; the format is explained in
The LaTeX Companion, and a tutorial is available
from CTAN (which comes with skeleton .dtx and
.ins files).
Composition of .dtx files is supported in emacs by
AUC-TeX.
Another useful way of generating .dtx files is to write the
documentation and the code separately, and then to combine them using
the makedtx system. This technique has particular value in
that the documentation file can be used separately to generate
HTML output; it is often quite difficult to make
LaTeX to HTML conversion tools deal
with .dtx files, since they use an unusual class file.
The .dtx files are not used by LaTeX after they have been
processed to produce .sty or .cls (or whatever)
files. They need not be kept with the working system; however, for
many packages the .dtx file is the primary source of
documentation, so you may want to keep .dtx files elsewhere.
An interesting sideline to the story of .dtx files is the
docmfp package, which extends the model of the doc
package to
Metafont and MetaPost,
thus permitting documented distribution of bundles containing code for
Metafont and MetaPost together with related LaTeX code.
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=dtx