Default anchor name (--a1):
top: 50 left: 0
a1.bottom: 50 a1.left: 0
Explicit anchor name (--a2) overrides default:
top: 250 left: 300
a2.bottom: 250 a2.left: 300
Mixed default and explicit:
top: 50 left: 300
a1.bottom: 50 a2.left: 300
No position-anchor, explicit name only:
top: 250 left: 300
a2.bottom: 250 a2.left: 300