The W3C GRDDL Working Group has updated the working draft of a GRDDL Primer. According to the draft,
GRDDL provides an inexpensive set of mechanisms for bootstrapping RDF content from XML and XHTML. GRDDL does this by shifting the burden of formulating RDF away from the author to transformation algorithms written specifically for XML dialects such as XHTML. In this document the term HTML is used to refer to the XHTML dialect of HTML.
GRDDL works through associating transformations with an individual document either through direct inclusion of references or indirectly through profile and namespace documents. For XML dialects the transformations are commonly expressed using XSLT 1.0, although other methods are permissible. Generally, if the transformation can be fully expressed in XSLT 1.0 then it is preferable to use that format since GRDDL processors should be capable of interpreting an XSLT 1.0 document.
While anyone can create a transformation, a standard transform library has been provided that can extract RDF that's embedded directly in XML or HTML using
<rdf:RDF>tags as well as extract any profile transformations. GRDDL transformations can be made for almost any dialect, including microformats.
