integrated document editing environment for TeX etc.

 AUCTeX is a comprehensive customizable integrated environment for writing
 input files for TeX/LaTeX/ConTeXt/Texinfo using GNU Emacs. Currently
 XEmacs ships with its own AUCTeX version.
 .
 It supports processing source files by running TeX and related tools
 (such as output filters, post processors for generating indices and
 bibliographies, and viewers) from inside Emacs. AUCTeX allows browsing
 through the errors reported by TeX, while it moves the cursor directly to
 the reported error, and displays some documentation for that particular
 error. This will even work when the document is spread over several
 files.
 .
 AUCTeX can automatically indent LaTeX source, either line by line or for
 an entire document, and has a special outline feature which can greatly
 assist in getting an overview of a document.
 .
 AUCTeX is written entirely in Emacs Lisp, and may therefore be enhanced
 with new features for specific needs. It comes with a large range of
 handy Emacs macros. It is a GNU project, and documentation for all its
 features is accessible via the Emacs info browser.