I am a bit concerned about duplication - if the same PA is in the parent and child, we'll have to test it (`canRead()`) twice on every SpEL evaluation where this PA doesn't support the expression.

We somehow need to weed out duplicate PAs - we can't just use class name because it might be the same class but configured differently.

I think the Registrar has to keep track of bean names and use the last one wins strategy (and we'd require an id/name on `<bean/>` within the `<spel-property-accessors/>` element (or the id via the ref).