loadXML with string
<!DOCTYPE page [
<!ENTITY ent1 "internal">
<!ENTITY ent2 SYSTEM "test2.xml">
will cause request to URL test2.xml (resolved against URI of the current page).
So Yes there is network activity with loading strings !.
Anyway even this scenario seems to behave synchronously (loadXml is blocking) even with async=true ;-)
"More on XML entities", and "Damned Defaults" are comming soon.... keep in touch