if this change results in a touch to every point of use anyways, can you also change the members to TitleCase?

I noticed, that the upper case strings are used accross the skin XML files. Therefore the string must remain upper case for backward compatibility.
PS: I just added a debug assert, which worked;-)

Now we have to decide, should we switch to Q_ENUM or should we rename to TitelCase?
Since Q_ENUM adds a overhead, I would prefer to rename and implement these two functions otherwise.

Since Q_ENUM adds a overhead

Out of curiosity, in what sense? From what I can tell, it only adds a little bit of compilation time due to the MOC.

Yes, the class must be a QObject and the MOC compilation comes on top.

The QObject could be avoided if the enum was moved to a namespace technically. Though I'm fine with leaving it as a plain enum class for now. Its unlikely that this enum would need to get exposed to the QML environment anyways (which is where the biggest value of a QEnum lies IMO).

This enum is only used in our legacy widgets. A use with QML is highly unlikely.