currently, file installation is triggered by setting the qbs.install property within Groups.

particularly within the context of QBS-942, it would make sense to simply put the Group inside the Export item instead, thus generalizing "installs" to "exports".
then, a single "installed" property on the whole Export item would decide whether the Export is internal (available only to other Products within the Project), or is actually installed.

FIXME: the syntax of installs was changed once already. investigate what was wrong with the previous approach and why the current one was chosen in particular.