Checkpoint 4.3 - XML/XSLT
Provide explicit human readable definitions for markup semantics
XML Accessibility Guidelines
Guideline 4: Document and export semantics
Informative, unambiguous documentation supports use and ongoing maintenance of coding structures. Where a schema is well documented, the interpretation of the semantics will be closer to the intention of the author and the shared understanding of the document is more likely. This in turn leads to a better and more exact product available to the end user.
Include human-readable annotation for XML elements as appropriate
The original source of this information is located on the W3C web site (www.w3.org/TR/xag#cp4_4)