"The Text Encoding Initiative (TEI) Guidelines are an international and interdisciplinary standard that enables libraries, museums, publishers, and individual scholars to represent a variety of literary and linguistic texts for online research, teaching, and preservation." Many of the following sites reference the Text Encoding Initiative.
This paper by Carrie Griffin and Julianne Nyhan, University College Cork, describes the production of electronic versions of medieval works. It discusses markup languages and their use in the humanities.
The project goal is described as "creating accurately keyboarded and SGML/XML encoded text editions for a significant portion of the EEBO corpus." There is a page with "current staff" that might provide useful contacts.
This site provides an overview of the ETCSL project, and has links to the main project site and technical information.
This site discusses a version of XML has been designed specifically for marking up the Bible.
This short article explains how literary scholars can use XML.
This article describes how Slovenian literature is being presented in a digital format, with several forms of the same text encoded and linked into a single edition using XML and the TEI Guidelines.
This is another overview page that describes the use of XML to markup ancient texts. There are a number of different projects mentioned on this page, with links to each project's main web site.
"The Repertorium of Old Bulgarian Literature and Letters was conceived as an archival repository capable of encoding and preserving in SGML (and, subsequently, XML) format archeographic, palaeographic, codicological, textological, and literary-historical data concerning original and translated medieval texts represented in Balkan Cyrillic manuscripts."