private void verifyDouble(String id, String val) {
        try {
            verifyDouble(id, Double.parseDouble(val));
        } catch (NumberFormatException e) {
            defFail(id, val, "double", e);
        }
    }
Returns the root ConfigDefinition, might be this.
config/src/main/java/com/yahoo/vespa/config/ConfigDefinition.java