A collection binding whose membership also depends on a cross-condition guard, so the candidates cannot be reduced until a token is known.
@type t() :: %Rete.Network.Node.AccumulateJoin{ alpha_code: atom(), coll_binding: atom() | nil, filter: fun(), filter_code: atom(), id: non_neg_integer() | nil, join_bind: [atom()], new_bind: [atom()], propagates_empty?: boolean(), type: atom() }