How to select descendent para, but not descendent para of descendent para ?

Hello

I have a tree of <var> nodes that can include other <var> nodes that can 
include other <var> nodes ...

I would like to allow <var> nodes to also be descendants of their parent 
<var>, not necessarily immediate children, so the XML tree may have more 
levels of nesting than the level of nesting of <var> nodes. The levels 
with nodes other than <var> are simply ignored, and only their <var> 
children are used in my application.

Is there a way to select the first-descendant, that will get me all 
descendant <var> node that have no <var> ancestor other then the context 
node and its ancestors ?

Or to put it another way, is it possible to select descendant <var> 
nodes, but not descendant <var> nodes included in descendant <var> nodes ?

Thank you,
Timothy Madden