private static boolean validName(String name) {
        if (name == null) return false;
        return namePattern.matcher(name).matches();
    }
Builds a {@link ConfigPayloadBuilder} representing the input 'config' xml element.

@param configE the 'config' xml element
@return a new payload builder built from xml
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/DomConfigPayloadBuilder.java