Checkpoint 2.2 - XML/XSLT
Separate presentation from structure in XML grammars and subsequent documents
XML Accessibility Guidelines
Guideline 2: Create semantically-rich languages
XML DTDs and Schemas that do not stipulate presentation elements and attributes in the markup support the flexibility of user-specified presentation of the document.
Do not include presentational elements or attributes in the XML DTD or Schema
The original source of this information is located on the W3C web site (www.w3.org/TR/xag#cp2_2)