Editing TeX (section)

===Macro language===

TeX documents are written and programmed using an unusual macro language. Broadly speaking, the running of this macro language involves expansion and execution stages which do not interact directly. Expansion includes both literal expansion of macro definitions as well as conditional branching, and execution involves such tasks as setting variables/registers and the actual typesetting process of adding glyphs to boxes.

The definition of a macro not only includes a list of commands but also the syntax of the call. It differs with most widely used [[lexical preprocessor]]s like [[M4 (computer language)|M4]], in that the body of a macro gets tokenized at definition time.

The TeX macro language has been used to write larger document production systems, most notably including LaTeX and ConTeXt.