[quote user="Jon Summers"]Each has its 'origin' at a different corner. The tags behave as you describe. What created those 'origins'?[/quote]
That's just how I drew the shapes, the red dot is located at the first vertex of each shape.
[quote user="Jon Summers"]If an element doesn't have an assoc. point already, how does mdlTag_create know what to do?[/quote]
The base element doesn't need to "have" anything; mdlAssoc_createOrigin will be called with the ElementId of the base element, and an assoc point dependency linkage will be added to the tag element. The place tag tool computes the offset by subtracting the evaluated assoc point location from the placement/accept point.