code: private Map<String, String> getReferences(Attributes attributes, String attributeName) {
          String attribute = attributes.getString(attributeName);
          Set<String> references = new HashSet<>();
          if (attribute != null && !attribute.trim().isEmpty()) {
              references.addAll(asList(attribute.split("\\s*,\\s*")));
          }
          Map<String, String> rules = new HashMap<>();
          for (String reference : references) {
              Matcher matcher = DEPENDENCY_PATTERN.matcher(reference);
              if (matcher.matches()) {
                  String id = matcher.group(1);
                  String referenceValue = matcher.group(3);
                  rules.put(id, referenceValue);
              }
          }
          return rules;
      }
docs: Get reference declarations for an attribute from a map of attributes.
  
  @param attributes
  The map of attributes.
  @param attributeName
  The name of the attribute.
  @return A map containing the ids of the references as keys and their
  associated values (optional).