AFAIR, they match the mkspecs that you can find in your Qt installation.

Great !

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Since this is pretty old, the solution is to at the bottom of the .pri file to use the export function. For every QMAKE key word you need an export for it.
In my above example I should append the following to the bottom:

export(PRE_TARGETDEPS)
export(QMAKE_EXTRA_TARGETS)