private static FederationOptions federationOptions(FederationConfig.Target.SearchChain searchChain) {
        return new FederationOptions().
                setOptional(searchChain.optional()).
                setUseByDefault(searchChain.useByDefault()).
                setTimeoutInMilliseconds(searchChain.timeoutMillis()).
                setRequestTimeoutInMilliseconds(searchChain.requestTimeoutMillis());
    }
The name of the query property containing the source name added to the query to each source by this
container-search/src/main/java/com/yahoo/search/federation/FederationSearcher.java