Representing nested fields

[TwiceII]

Hey! First of all, I want to thank you for this awesome library, I have been using it lately and find it really useful.
One thing I wonder about is - how should one declare fields that are nested? I can represent them as separate entities, but sometimes they are not really worth it.
Suppose that I want to declare a schema for some Event in Event Sourcing style app. The Event entity has fields like id, type, timestamp which are flat fields, but also a payload which is nested and has its own fields. Making separate Payload entity is kinda awkward because:

1. Semantically payload is just a part of Event entity.
2. I don't want all the downstream Hodur plugins to treat it as "real" entity and create tables etc for them.