docs: public Whitelist addProtocols(String tag, String attribute, String... protocols) {
          Validate.notEmpty(tag);
          Validate.notEmpty(attribute);
          Validate.notNull(protocols);
  
          TagName tagName = TagName.valueOf(tag);
          AttributeKey attrKey = AttributeKey.valueOf(attribute);
          Map<AttributeKey, Set<Protocol>> attrMap;
          Set<Protocol> protSet;
  
          if (this.protocols.containsKey(tagName)) {
              attrMap = this.protocols.get(tagName);
          } else {
              attrMap = new HashMap<>();
              this.protocols.put(tagName, attrMap);
          }
          if (attrMap.containsKey(attrKey)) {
              protSet = attrMap.get(attrKey);
          } else {
              protSet = new HashSet<>();
              attrMap.put(attrKey, protSet);
          }
          for (String protocol : protocols) {
              Validate.notEmpty(protocol);
              Protocol prot = Protocol.valueOf(protocol);
              protSet.add(prot);
          }
          return this;
      }