In order to create a facet based on multiple folder, the hippo:docbase property of the facet has to be filled with a comma separated list of uuid.
The hippo console gives a wrong feedback when entering a comma separated list of uuids i.e.
"Not a valid JCR identifier"
As suggested by Ard Scrijvers feedback could be improved:
"in case of testing hippo:docbase that when it seems an invalid docbase, we test whether it happens to be a comma separated list of uuids. "