I haven't ever actually used APP, but I don't have problems with it not having any parents. APP is a member of %m.edit;, which in turn is included in %m.phrase;, which in turn is included in %m.paraContent; (among others). Thus, APP can go most anywhere. It is interesting to note, though, that the P3 text lists "[none]" as the "May occur within" for APP (p. 864). I have successfully validated a file with an APP inside a P element using Author/Editor on the Mac.