There is no way to document that a QML property in a QML component is read-only or read-write.

For QML elements, the read-only/read-write status of a QML property is determined by traversing the C++ class hierarchy for the C++ class that instantiates the QML element. A Q_PROPERTY macro is found that has the same name as the QML property that either has a write method or not, and that determines whether the QML property is read-only or read-write.

But for QML components, there is no C++ class specified for the QML component, so there is no C++ class hierarchy to search for a corresponding Q_PROPERTY macro, so we need a \readonly command to be able to distinguish read-only from read-write for QML properties of QML components.