this implementation replaces the former non standard node schema, and works in a similar
way (the schema is put in a separated node instead of a special field, thus it will now
work with most/all PubSub services, and not only SàT PubSub).
The implementation has been done in a way that nothing should be changed in frontends
(bridge methods names and arguments stay the same). The nodes are modified, but if values
are taken from backend, it's automatically adapted.
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