Hi,
Mallard [1] is an XML-based markup language for topic-based documentation that is extensively used by the GNOME Documentation Project. Attached is a proposed patch that implements a filetype definition file for this language and adds appropriate entries to the filetype_extensions.conf file.
The filetype definition file is based on the latest version of the Mallard 1.0 DRAFT [2] as of Moday, 11 February 2013, and is also available in my GitHub repository [3]. Also available are my snippets for this language [4].
[1] http://www.projectmallard.org/ [2] http://projectmallard.org/1.0/index.html [3] https://github.com/jhradilek/geany-syntax [4] https://github.com/jhradilek/geany-snippets
Cheers,