See the Language Specification in our Eclipse-based Help DITA Infocenter with excellent full-text search.
ditamap.com has a frameset view of the language specification.
gotAPI.com has an excellent frameset view with progressive search.
DITA 1.1 is now approved. The DITA Version 1.1 release consists of an architectural specification, a language specification, a set of DTDs, and an equivalent set of Schemas.