This test expects XPTY0019 but I think it can equally well raise XPTY0018.

The test is of the form $a/f(.)/x

where f(.) sometimes returns a node and sometimes returns an atomic value.

So there are two errors: the RHS of the first "/" operator is a mix of nodes and atomic values; and the LHS of the second "/" operator is not all nodes; hence two possible error codes, depending on which is detected first.