A common problem for controls is that when the business logic is implemented in a C++ "base" type and the visual parts in a QML "sub" type, enum values provided by the C++ type cannot be accessed by the QML type name.

Example: a TextField control that inherits QQuickTextInput.

// TextField.qml
TextInput {
    id: control
    implicitWidth: ...
    implicitHeight: ...
    Rectangle {
        id: background
        z: -1
    }
}

Application code cannot use eg. TextField.Password but must use TextInput.Password instead:

TextField {
    // echoMode: TextField.Password // "ReferenceError: TextField is not defined"
    // vs.
    echoMode: TextInput.Password // :(
}