This proviso is called conditionality: the buyer needs to know they will continue to get what they have paid for. It is a range of financing arrangements for the conservation and sustainable use of natural ecosystems, such as forests, to ensure that the cost to the environment is paid for. It is not, therefore, one model to be universally applied, but rather a series of schemes which can be considered for application to particular circumstances, whether or not they exactly conform to the CBD or UNECE definition.