Emacs provides special major modes for editing files written in TeX and its related formats. TeX is a powerful text formatter written by Donald Knuth; like GNU Emacs, it is free software. LaTeX is a simplified input format for TeX, implemented using TeX macros. DocTeX is a special file format in which the LaTeX sources are written, combining sources with documentation. SliTeX is an obsolete special form of LaTeX.1
TeX mode has four variants: Plain TeX mode, LaTeX mode,
DocTeX mode, and SliTeX mode. These distinct major modes differ
only slightly, and are designed for editing the four different
formats. Emacs selects the appropriate mode by looking at the
contents of the buffer. (This is done by the
which is normally called automatically when you visit a TeX-like
file. See Choosing Modes.) If the contents are insufficient to
determine this, Emacs chooses the mode specified by the variable
tex-default-mode; its default value is
Emacs does not guess right, you can select the correct variant of
TeX mode using the command M-x plain-tex-mode, M-x
latex-mode, M-x slitex-mode, or doctex-mode.
The following sections document the features of TeX mode and its variants. There are several other TeX-related Emacs packages, which are not documented in this manual:
 It has been replaced by the ‘slides’ document class, which comes with LaTeX.