HTML5 UI flow builder --> XML --> Bonita Engine

Dear Bonita friends,
we need a little help.

We would like to implement the reverse of a usual Bonita UI:
* We would like to create a flow with an HTML5 frontend builder, unrelated to Bonita.
* We then want to pass that flow's XML to the Bonita engine. Some flow settings, attributes will be a default.
* Hopefully, the Bonita engine will run the flow.

Now, the questions:
1. what XML structure (specifics) is the Bonita engine expecting in order for the flow (created with an HTML5 builder) to be considered executable?
2. do you know of any bridge that can take a simplistic flow (designed with a UI builder), attach some defaults, and pass that to the Bonita engine?

I wish everyone a nice weekend, and thank you already for any and all ideas!
Adrian