Namespace arguments, namespace routing language

More complex xml languages have various 
models for how they handle unknown markup,  
and unknown namespaces. 

the following three examples, probably not 
100% correct:

html(not xml but what the hell):
ignore unknown markup, unknown attributes, 
make attributes available to Document Object 
Model, parse subtrees.

svg: ignore unknown namespaced markup, do 
not parse subtree, ignore namespaced 
attributes, parse element.

xsl-t:
unknown markup without a namespace within 
the xsl namespaced stylesheet element is not 
allowed. 

namespaced markup within the xsl namespaced 
stylesheet element is ignored, but is 
available to the xslt via document('')



Now the thing that's been bugging me is I 
would like to have a language that provides 
me the syntactical structure to define these 
ways of handling namespaced and unknown 
markup without throwing all validation out 
the window. The namespace routing language 
looks like it comes close but it doesn't 
seem to have everything I need (or is that 
want) am I correct in saying that this 
language does not exist and if I want it I 
better make it or does anyone know of 
anything that does what I want?