Re: Type of a variable containing values of mixed type

This question has been on my TODO list to ask the folks at MulberryTech 
XSL List for quite some time.

I think this came about in XPath DM 3.0 regarding xs:numeric as per spec 
ref:

http://www.w3.org/TR/xpath-datamodel-3/#types-hierarchy

In the type hierachy xs:numeric now appears for the first time spec-wise 
(I believe) and it's on the right-hand side under "union types".

Mathematically this seems inconsistent with respect to xs:anyAtomicType 
given that it as a diagrammed type itself appears on the left-hand side 
of the type hierarchy diagram and so does not identify itself as a union 
type. But surely xs:anyAtomicType is in fact a union type 
(set-theoretically/type-theoretically speaking). So with respect to 
"union/non-union" reasoning which is correct xs:anyAtomicType or 
xs:numeric as far as the diagram goes? Or, rephasing, why is xs:numeric 
treated somehow differently to xs:anyAtomicType?

On the other hand, perhaps this is all to do with some practical reason 
for injecting xs:numeric into the XPath DM 3.0 type hierarchy as a union 
type so as not to disaffect the status quo?

Any thoughts/insight from XSL List community?

Justin Johansson

Twitter: ** b*@MartianOdyssey* <https://twitter.com/MartianOdyssey> : 
Project Clockwork: My invention of the fastest and most extensible XPath 
engine for the JVM (or so I aspire to).