I can have a new Thing point back to the creating Thing

Summary: I've found that I often wind up with parent-child relationships between Things; in particular, I often want to put a button on Parent that says, "Create a new Child". All of which works decently well (using _createButton or _createInstanceLink), but with one problem: the Child doesn't start out with the pointer back to the Parent. I have to set that back-link manually, which is a hassle.

Solution has turned out to be adding a defining context parameter to _createInstanceLink, which says what the back-link Property is. If that's given, it automatically sets the back-link at creation time.