[CONNECT C++] Using a WhereCriterion to filter out schemas

I'm looking at elements that have XAttributes on them. I can create a ECQuery to find instances on an element. When I look at what is found, it is not uncommon to find multiple Classes on an element. For example:

[DgnElementSchema:LineElement]
[DgnCustomItemTypes_SRSFeature:Air__x0020__Tunnel]

I'm interested in the 'SRSFeature' XAttributes. Is it possible to (and how would you) set up a WhereCriterion to restrict the ECQuery to return only ones from the 'DgnCustomItemTypes_SRSFeature' schema? USe CreateStringFilter()?

Bruce