The documentation for MathJax is available here for the current version, as well as older versions of MathJax. The links below take you to the Tables of Contents for the documentation for the indicated versions of MathJax.
- MathJax v1.1 documentation (current version)
- MathJax v1.0 documentation
The MathJax documentation also is part of the MathJax source repository, so if you download a copy of MathJax, the documentation will be included with that in the docs/html directory.