I stumbled across this code in `kdl-rs`, and calling `KdlDiagnostic::severity()` returns `None` instead of the value stored in `pub severity`!  This works (and is what the documentation shows):  But in that case, the severity is fixed to be `Warning` and doesn't look at `severity` at all! I think the docs may benefit from more clearly showing the correct syntax for doing this sort of thing (if the derive macro supports it at all!)