The TEI Guidelines
The TEI Guidelines, which collectively define an XML format, are the defining output of the community of practice. The format differs from other well-known open formats for text (such as HTML and OpenDocument) in that it's primarily semantic rather than presentational; the semantics and interpretation of every tag and attribute are specified. Some 500 different textual components and concepts (word, sentence, character, glyph, person, etc.); each is grounded in one or more academic discipline and examples are given.
Read more about this topic: ODD (Text Encoding Initiative)