https://doc.qt.io/archives/qt-4.8/qmake-environment-reference.html#installs
To help in the install process qmake has the concept of a install set.
It looks like a install set have members, i.e. path, files and extra:
documentation.path = /usr/local/program/doc
documentation.files = docs/*
Are there other members?
What members need to be set in order to consider the install set fully described?
Where the create_docs come from in the case below
unix:documentation.extra = create_docs; mv master.doc toc.doc
QMake is documented... not. Whenever you want to know something you go browse source code. In this case, it's in qmake/generators/makefile.cpp, function Makefilegenerator::writeInstalls().
As we can see, it's path, files, base, extra, CONFIG, uninstall and depends. extra (or commands) is an arbitrary line to insert at the top.
What members need to be set in order to consider the install set fully described?
QMake is Makefile generator. Whatever human does it simply outputs some Makefile. Whether it will work or not, that's a human's problem.