Documented LaTeX sources (`dtx` files)

LaTeX 2e, and many contributed LaTeX macro packages, are written in a literate programming style, with source and documentation in the same file. This format in fact originated before the days of the LaTeX project as one of the “Mainz” series of packages. A documented source file conventionally has the suffix `dtx`, and will normally be ‘stripped’ before use with LaTeX; an installation (`ins`) file is normally provided, to automate this process of removing comments for speed of loading. If the `ins` file is available, you may process it with LaTeX to produce the package (and, often, auxiliary files).

Output should look something like:

```Generating file(s) ./foo.sty

Processing file foo.dtx (package) -> foo.sty
File foo.dtx ended by \endinput.
Lines  processed: 2336
Comments removed: 1336
Comments  passed: 2
Codelines passed: 972
```
The lines “Processing … ended by `\endinput`” may be repeated if the `dtx` file provides more than one ‘unpacked’ file.

To read the comments “as a document”, you can run LaTeX on the `dtx` file to produce a nicely formatted version of the documented code. (Most LaTeX packages on CTAN, nowadays, already have PDF of the result of processing the `dtx` file, as “documentation”.)

Several packages may be included in one `dtx` file, with conditional sections, and there are facilities for indexes of macros, etc. All of this mélange is sorted out by directives in the `ins` file; conventional indexing utilities may be necessary for “full” output.

Anyone may 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.

The (unix-based) script dtxgen generates a proforma basic `dtx` file, which could be useful when starting a new project.

Another route to an `dtx` file 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 sty2dtx system goes one step further: it attempts to create a `dtx` file from a ‘normal’ `sty` file with comments. It works well, in some circumstances, but can become confused by comments that aspire to “structure” (e.g., tabular material, as in many older packages’ file headers).

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.

AUC-TeX
auctex
clsguide.pdf
clsguide
docmfp.sty
docmfp
docstrip.tex
Part of the LaTeX distribution
DTX tutorial
dtxtut
dtxgen
dtxgen
makedtx
makedtx
sty2dtx
sty2dtx

This answer last edited: 2014-06-03