@Override
        public String toString() {
            if (validators == null) return "";
            StringBuilder desc = new StringBuilder();
            for (Validator v: validators) {
                if (desc.length() > 0) {
                    desc.append(',').append(' ');
                }
                desc.append(v);
            }
            return desc.toString();
        }
A numeric range that checks both the upper (inclusive) and lower bound
clients/src/main/java/org/apache/kafka/common/config/ConfigDef.java