GRDDL is a mechanism for Gleaning Resource Descriptions from Dialects of Languages. This GRDDL specification introduces markup based on existing standards for declaring that an XML document includes data compatible with the Resource Description Framework (RDF) and for linking to algorithms (typically represented in XSLT), for extracting this data from the document.
The markup includes a namespace-qualified attribute for use in general-purpose XML documents and a profile-qualified link relationship for use in valid XHTML documents. The GRDDL mechanism also allows an XML namespace document (or XHTML profile document) to declare that every document associated with that namespace (or profile) includes gleanable data and for linking to an algorithm for gleaning the data.
A corresponding GRDDL Use Case Working Draft provides motivating examples. A GRDDL Primer demonstrates the mechanism on XHTML documents which include widely-deployed dialects known as microformats. A GRDDL Test Cases document illustrates specific issues in this design and provides materials to aid in test-driven development of GRDDL-aware agents.From: Gleaning Resource Descriptions from Dialects of Languages, W3C Proposed Recommendation, 16 July 2007