Changes

In this article, I have mentioned only one aspect of programming TeX: macros that manipulate their input and output some text to the main TeX stream. Many other kinds of manipulations are possible: luaTeX provides access to TeX boxes, token lists, dimensions, glues, catcodes, direction parameters, math parameters, etc. The details can be found in the [http://www.luatex.org/documentation.html luaTeX manual].