How to define your own custom facets? I could not find anything in the Studio for that, nor in the documentation (https://doc.nuxeo.com/nxdoc/available-facets/).
I want to define a custom facet 'InvoiceFacet' that I can assign to existing documents, since changing a document type afterward does not seem to be possible, according to this older forum entry: https://answers.nuxeo.com/general/q/5ed5ce59c3e54e719bfb2ba105bfb385/Change-Document-type
Thanks!
