Preference level interaction

[squarooticus]

Therefore, the transport system SHOULD race the path first, ignoring the protocol preference if a specific protocol does not work on the path.

Presumably this is true only if:

• A candidate protocol has no property marked Prohibit
• All candidate protocols have every property marked Require

I know we rejected any attempt to allow the user to encode preference ordering in the transport selection properties, but should a single order be normatively specified in this document? Right now, there is only one rule and that is "prefer paths over protocol properties", which might be fine, but it's unclear how this would work in practice.