If I use the \include command then I get:

/home/xxx/dev/qt/qt5/qtlocation/src/location/places/qplace.cpp:62: warning: Unknown command '\include'
[The command '\include' was renamed '\input' by the configuration file. Use the new name.]

Now, if I replace \include by \input (based on the error message above) then the error changes to:

/home/xxx/dev/qt/qt5/qtlocation/src/location/places/qplace.cpp:63: warning: Cannot find qdoc include file 'place-definition.qdocinc'

I just about put the file everywhere (snippts, src, examples and the root doc dir).

The \snippet command is not an alternative as it assumes that the to-be-included text is source code only.