combine — combine parallel paths into a single output
( => ... => ...) | ...
combine operator merges inputs from multiple upstream legs of
the dataflow path into a single output. The order of values in the combined
output is undefined.
You need not explicit reference the operator with any text. Instead, the mere existence of a merge point in the flow graph implies its existence and its semantics of undefined merge order.
Copy input to two paths and combine with the implied operator
echo '1 2' | zq -z 'fork (=>pass =>pass) | sort this' -