protected String getConfigValue(ConfigKey key, String headerName) {
        switch (headerName) {
            case "Name":
                return key.name;
            case "Description":
                return key.documentation;
            case "Type":
                return key.type.toString().toLowerCase(Locale.ROOT);
            case "Default":
                if (key.hasDefault()) {
                    if (key.defaultValue == null)
                        return "null";
                    String defaultValueStr = convertToString(key.defaultValue, key.type);
                    if (defaultValueStr.isEmpty())
                        return "\"\"";
                    else {
                        String suffix = "";
                        if (key.name.endsWith(".bytes")) {
                            suffix = niceMemoryUnits(((Number) key.defaultValue).longValue());
                        } else if (key.name.endsWith(".ms")) {
                            suffix = niceTimeUnits(((Number) key.defaultValue).longValue());
                        }
                        return defaultValueStr + suffix;
                    }
                } else
                    return "";
            case "Valid Values":
                return key.validator != null ? key.validator.toString() : "";
            case "Importance":
                return key.importance.toString().toLowerCase(Locale.ROOT);
            default:
                throw new RuntimeException("Can't find value for header '" + headerName + "' in " + key.name);
        }
    }
A numeric range that checks both the upper (inclusive) and lower bound
clients/src/main/java/org/apache/kafka/common/config/ConfigDef.java