Before looking at TeX itself, you may want to look at a few smaller programs. One of them is TANGLE
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I also have an annotated version of this program, here – will move the content onto this page eventually.
To read the program, click on "Fetch modules" below.That's the end of this page. If you have any feedback about anything on this site, you can contact me here. To go back to the top-level page (if you are not on it already), click here.