tool for defining informal markup languages ?

[r.shimmin]

There exist a number of related informal markup languages whose design
philosophy is to use terse, easily human-entered and human-read tags,
that are intended to be converted by software into some flavour of SGML
or XML. The markup languages used for editing on many wikis are the
most prominent examples.

Can anyone tell me whether there exists a tool that would allow me to
define such a language, and the xml elements that the "informal"
elements are intended to represent, and emit, say, a perl script for
converting documents written in the informal into XML documents.

 

[Stefan Ram]

Can anyone tell me whether there exists a tool that would allow
me to define such a language,

To define such a language, a specification would have to be
written for its syntax and semantics. This requires a pencil
or a text editor or so.

and the xml elements that the "informal" elements are intended
to represent, and emit, say, a perl script for converting
documents written in the informal into XML documents.

A major part of the work should be making the design decisions
and writing the specification.

The best approach might be to use one of the existing
plain-text-markup-languages. If the source code for a
converter is available for them, it might be used and
modified to derive a similar language.

The plain-text-markup-languages I am aware of are:

http://docutils.sourceforge.net/rst.html
http://www.python.org/sigs/doc-sig/stext.html
http://textism.com/tools/textile/
http://www.textism.com/tools/textile/
http://tikiwiki.org/tiki-print.php?page=RFCWiki
http://daringfireball.net/projects/markdown/
http://www.maplefish.com/todd/aft.html
http://www.xmlmind.com/aptconvert.html

From the viewpoint of computer science, any plain-text
markup language is a "formal language".