(17)For the purpose of legal clarity this Directive should lay down a definition of a sales contract and also clearly define its scope. The scope of this Directive should also cover contracts for goods that are yet to be produced or manufactured, including under the consumer's specifications. Furthermore, an installation of the goods could fall within the scope of this Directive if the installation forms part of the sales contract and has to be carried out by the seller or under the seller's responsibility. Where a contract includes elements of both sales of goods and provision of services, it should be left to national law to determine whether the whole contract can be classified as a sales contract within the meaning of this Directive.