Feature request: add more context to visitor params

[acgreek]

I would like to write a plugin that validates that specific fields exist at specific indexes, with correct types

We have a common Event type where field index 1 must always be a timestamp and field 2 must be meta sub message. I want to be able to write a plugin that validates when someone adds a new Event type, those two fields exist with the required index and types.

This allows our down stream apps to add Event types before our backend knows how to process them completely, and can at least process the common fields.

[acgreek]

NM, figured out how to do this