I'm currently writing an xslt extension and I need to detemine between document and properties.  I wanted to use the isDoc attribute however the xpathnavigator.GetAttribute method returns an empty string if the attribute is not found - the same value that the isDoc property will contain if it exists. 

Is there a specific reason for this?

Is it safe for me to evaluate the id attribute instead to determine whether a node is a document or property? (i.e. I presume that only document nodes will have id's and proerpties will not).