.dtx files)LaTeX2e, and many support macro packages, are now written in a
literate programming style,
with source and documentation in the
same file. This format, known as 'doc', in fact originated before the
days of the LaTeX project as one of the "Mainz" series of
packages. The documented sources conventionally have the suffix
.dtx, and should normally be stripped of documentation
before use with LaTeX. Alternatively you can run LaTeX on a
.dtx file to produce a nicely formatted version of the
documented code. An installation script (with suffix
.ins) is usually provided, which needs the standard LaTeX2e
docstrip package (among other things, the installation
process strips all the comments that make up the documentation for
speed when loading the file into a running LaTeX system). Several
packages can be included in one .dtx file, with conditional
sections, and there facilities for indices of macros etc. Anyone can
write .dtx files; the format is explained in
The LaTeX Companion
(see books on TeX), and a tutorial is
available from CTAN (which comes with skeleton .dtx and
.ins files).
Composition of .dtx files is supported in emacs by
Matt Swift's swiftex system: it provides a
doc-tex mode which treats .dtx files rather
better than AUC-TeX manages.
.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