The latest version of the DITA Open Toolkit supports the DITA 1.2 specification. Initial support for this specification was added in version 1.5 of the toolkit; versions 1.5.1 and 1.5.2 contain minor modifications to keep up with the latest drafts. The specification itself was approved at approximately the same time as DITA-OT 1.5.2, which contains the final versions of the DTD and Schemas.
Earlier versions of the DITA Open Toolkit contained a subset of the specification material, including descriptions of each DITA element. This material was shipped in source, CHM and PDF format. This was possible in part because versions 1.0 and 1.1 of the DITA Specification contained two separate specification documents: one for the architectural specification, and one for the language specification.
In DITA 1.2, each of these has been considerably expanded, and the two have been combined into a single document. The overall document is much larger, and including the same set of material would double the size of the DITA-OT package. Rather than include that material in the package, we’ve provided the links below to the latest specification material.
To find detailed information about any of these features, see the specification documents at OASIS. The DITA Adoption Technical Committee has also produced several papers to describe individual new features. In general, the white papers are geared more towards DITA users and authors, while the specification is geared more towards tool implementors, though both may be useful for either audience. The DITA Adoption papers can be found from that TC’s main web page.