Altitude frame in mission-file vs. Location.h -> where I can find the translation?

Development Team
1

When reading a mission-file (*.waypoints), I receive the frame as
0 for ABSOLUTE,
3 for ABOVE_HOME,
10 for ABOVE_TERRAIN

In Location.h the enum class is defined in that way:

    /// enumeration of possible altitude types
    enum class AltFrame {
        ABSOLUTE = 0,
        ABOVE_HOME = 1,
        ABOVE_ORIGIN = 2,
        ABOVE_TERRAIN = 3
    };

I think I learned that the ABOVE_ORIGIN frame is an internal frame for ‘correction’ the altitude. So it seems to me that the above info is exhausting.
I’ve seen something like mavlink-ish format, but where I can find that translation?