Latest refinements and batch of questions:
 1  I gave up type subclassing, too much work and nobody seems excited

 2 should we have <fields/> and <getters/> or should <field/> <getter/> be directly under <bean/> ?

 3 should we have <groups/> or should <group/> be under <constraint/> directly?

 4 should we allow 
<element name"size">30</element> 
with the risk of people doing 
<element name"size">30<value>blah</value></element>
or should we mandate the use of value
<element name"size"><value>30</value></element> 

 5 if some people could look at the xsd and propose improvement, that'd be great.

I plan to introduce that in the spec tomorrow, so early feedback would be fantastic

XML represents a sample and XSD is the schema generated from the XML file and adjusted.