https://drafts.csswg.org/cssom-view/#dom-element-getboundingclientrect
If the list is empty return a static DOMRect object
What precisely does "static" mean here? Neither CSSOM View nor Geometry Interfaces seems to define staticness, either generally or in relation to DOMRect specifically. And the WebIDL static keyword doesn't seem applicable here.
Perhaps DOMRectReadOnly was intended?