- Conditions on which txs are accepted to mempool - Conditions on which txs are not accepted - Conditions on which txs are first accepted and later dropped (i.e. fees) - Size limitations - Behavior when mempool is full Most of mempool default behaviors are inherited from Substrate, but we want fraud proofs to have separate handling (see https://github.com/subspace/subspace/issues/2570 and https://github.com/subspace/subspace/issues/2567)