I downloaded DNG SDK and it contain full(?) source code to read and write DNG files
only closed (propriatary) code can be in XMP SDK subsection of DNG SDK
XMP= Extensible Metadata Platform
Adobe's Extensible Metadata Platform (XMP) is a labeling technology that allows you to embed data about a file, known as metadata, into the file itself. More information on how partners and standards are using XMP is available at the XMP website.
The XMP Toolkit allows you to integrate XMP functionality into your product or solution. It supports Macintosh, Windows, as well as UNIX and comes with samples, documentation, source code and project files. The XMP Toolkit is available under the BSD license.
hm. have BSD license forces to publish sources?