code: private void addRulesFromDocument(Document document) {
          NodeList ruleNodes = document.getElementsByTagName("rule");
          for (int i = 0; i < ruleNodes.getLength(); i++) {
              addRule(extractClassAttributeFromNode(ruleNodes.item(i)), extractPriorityAttributeFromNode(ruleNodes.item(i)));
          }
      }
docs: Walks through the {@link Document} and tries to instantiate and add a {@link Rule} instance for every listed
  rule to the rules contained in this {@link RuleSet}.
  
  @param document {@link Document} to read the rules from