static double extractExtensionOrdinal(Class clazz) {
        Extension extension = (Extension) clazz.getAnnotation(Extension.class);
        if (extension == null) {
            return 0.0;
        }
        return extension.ordinal();
    }
Describe Structure of the attributes, as required by the schema.
@param instance
     Object whose attributes will be described.
@param context
     Fully configured Jenkins object used as the starting point for this configuration.
@since 1.35
@return CNode describing the attributes.
plugin/src/main/java/io/jenkins/plugins/casc/Configurator.java