Should the fullscreen pre-lock condition also check for a pending fullscreen request?

[EdgarChen]

In Spec, the fullscreen pre-lock condition only mentions

A user agent SHOULD restrict the use of lock() to simple fullscreen documents as a pre-lock condition.

in 9. Interaction with Fullscreen API.

However, Chrome also allows the lock when there is pending fullscreen request, there was a webcompat report for this, so Gecko adopted the same behavior in bug 1744288. As some pages already rely on this behavior, perhaps we should define it more clearly into spec? If so, the spec should also define how to handle the lock if the pending fullscreen request is rejected.