UML-ish question

I came across something on a UML class diagram today that I have never
seen before and I'm wondering about the validity of it. The diagram
has a class which has an association with itself (a line coming out of
the class, making 2 90 degree turns and going back into itself).

Is that legal UML? If so, what does it mean? I think they are trying
to show an association between two instances of the class, which I
don't think belongs on the class diagram.

Any viewpoints?

Thanks
James

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