It looks like it's part of this extension, being for the :Real Name field, but it's a bit confusing when there's nothing to really explain this or what the extra field is for, besides a passing mention later on that JOIN has something to do with 3.1 extensions:
Link
It looks like it's part of this extension, being for the
:Real Name
field, but it's a bit confusing when there's nothing to really explain this or what the extra field is for, besides a passing mention later on that JOIN has something to do with 3.1 extensions: