XForms for HTML, RDFa and ARIA... and HTML5

What are the commonalities among XForms for HTML, RDFa and ARIA.
These seem to be the front-runners for either inclusion in HTML5, or 
inclusion of an extensibility mechanism in HTML5 to enable these to 
interoperate.

John M. Boyer, Ph.D.
STSM, Interactive Documents and Web 2.0 Applications
Chair, W3C Forms Working Group
Workplace, Portal and Collaboration Software
IBM Victoria Software Lab
E-Mail: boyerj@ca.ibm.com 

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