Attribute-only splat expressions, indicated by using the star symbol as
if it were an attribute, are inherited from HIL and are a limited sort of
splat that only works for walking through attributes in each item of its
source.
Later zcl will also get full splat expressions, whose syntax is using
the star symbol as if it were an _index_, which will generalize to
supporting _all_ postfix traversal operations, including indexing and
nested splats.
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