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Explanation: Or words to that effect. You seem to have given the answer in the note to your question.
This term sounds suspiciously similar to ‘vestiaire’, which is used by French barristers, and which I’ve seen debated before.
As such it is not a ‘pigeonhole’ for the communication of documents.
The ‘vestiaire’ is the position where they hang their formal togs for court appearances. They each have their own permanent place, which is numbered and it is this number by which they are identified/registered with the (Paris) bar.