### Reference documents

For TeX primitive commands a rather nice quick reference booklet, by John W. Shipman, is available; it’s arranged in the same way as the TeXbook. By contrast, you can view David Bausum’s list of TeX primitives alphabetically or arranged by “family”. Either way, the list has a link for each control sequence, that leads you to a detailed description, which includes page references to the TeXbook.

There doesn’t seem to be a reference that takes in Plain TeX as well as the primitive commands.

Similarly, there’s no completely reliable command-organised reference to LaTeX, but the NASA Hypertext Help with LaTeX is recently much improved. It still talks in LaTeX 2.09-isms in places, but it’s been updated for current LaTeX; there are a number of mirrors of the site, and it may be worth choosing a “local” one if you’re going to use it a lot.

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=ref-doc