private Collection<Source> buildSources(DeployState deployState, TreeConfigProducer<AnyConfigProducer> ancestor, Element providerElement) {
        List<Source> sources = new ArrayList<>();
        for (Element sourceElement : XML.getChildren(providerElement, "source")) {
            sources.add(new DomSourceBuilder(outerComponentTypeByComponentName).build(deployState, ancestor, sourceElement));
        }
        return sources;
    }
Retrieves all possible provider specific parameters
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/search/DomProviderBuilder.java