like for example in the following statement
doc.MyField = "bla"
Given that field names can be chosen by the programmer, I'm afraid the answer to your question is: No, there is no general rule for building a search for expanded name calls -- except if you can be sure that field names in an application always start with a defined prefix.
FWIW, this is one of the reasons why I never use expanded name calls in my code.
Feedback response number JSAK95KDZM created by Jochen Sack on 03/07/2013