Discovering permanent anchors

[martinthomson]

In the anchors section of the working mode there is a process for negotiating the creation of a permanent anchor. This is good, but that process does not describe how to discover whether a permanent anchor already exists. If it were possible to discover that an anchor is permanent, then there might be fewer requests.

I couldn't see any reference to a permanent anchor having been requested or executed either, nor could I see anything in fetch or html source, so I don't know whether this policy is in active use.