[lxml-dev] Use of XPathEvaluator object in extension functions?

Hi, I just looked through the documentation a bit and started rewriting xpath.txt for the new Namespace API. I never actually thought much about it, but the docs made me stumble over the fact that extension functions take the XPathEvaluator object as first parameter. I don't really know what that is good for. Has anyone used this feature so far? What purpose does it serve? When I rewrote the implementation, I introduced a 'ContextBuilder', which is now passed instead. I'm wondering if that can fulfil the original intention... Can anyone enlighten me? Stefan