Misleading/outdated documentation on enabling proprietary codecs

The documentation provided https://doc.qt.io/qt-5.10/qtwebengine-features.html on building Qt with proprietary codecs suggests a configuration option should be passed to qmake ("CONFIG+=-proprietary-codecs").  The documentation should be more clear, stating explicitly to call qmake as follows (with any additional desired parameters):

qmake -- -proprietary-codecs

Otherwise it doesn't configure appropriately, and one may be left trying to figure out why for some time.