they have to be clearly defined in international, not British or US regulations.
- for 'have to' I suggest 'should be', and the point I am making is that when things are not clear, clarify and if that is still confusing and you are really not sure, then stick with a procedural approach. We cannot expect a perfect harmonised world.
In your quote I assume all you needed was clearance to land - you clarified and got it.