private Set<String> read(Element spec, String name) {
        Set<String> symbols = new HashSet<>();
        symbols.addAll(XmlHelper.valuesFromElements(spec, name));
        symbols.addAll(XmlHelper.spaceSeparatedSymbolsFromAttribute(spec, name));

        return symbols;
    }
Builds Dependencies (provides, before, after) from an element.
@author Tony Vaagenes
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/chains/DependenciesBuilder.java