** Implement to create custom instances of 'ClientAsset'.** ** Producer instances should be contributed to the 'ClientAssetProducers' service:**** syntax: fantom ** @Contribute { serviceType=ClientAssetProducers# }** Void contributeAssetProducers(Configuration config, MyAssetProducer assetProducer) {** config["acme.myAssetProducer"] = assetProducer** }** ** Asset caching strategies, like Cold Feet, use the 'ClientAssetProducers' service to modify the client URLs of 'ClientAssets'. mixin ClientAssetProducer {** Creates a 'ClientAsset' from the given local URL.** ** Returns 'null' if the URL can not be mapped. abstract ClientAsset? produceAsset(Uri localUrl)}