An anonymous nested op-expression leg: composes inline as an intermediate
cell (its as id, or a positional id derived from the parent). Its own legs
are ref/compose, so the algebra reads as an expression tree.
An anonymous nested op-expression leg: composes inline as an intermediate
cell (its as id, or a positional id derived from the parent). Its own legs
are ref/compose, so the algebra reads as an expression tree.