I find the term "Master document" in the Settings tab of Advanced Find, to be an unintuitive name. The tooltip does, however, clarify things.
To me, "Master document" implies that only the master document is searched, not the children. I have trouble thinking of a short name to suggest as an alternative. I suggest "Master and included documents" or "Master and child documents". Note that the width of the widget should not increase much, because there is already the lengthy "Preserve first case on replace". Any thoughts? Scott