code: public Precondition create(String tagName) {
          Class<?> aClass = preconditions.get(tagName);
          if (aClass == null) {
              return null;
          }
          try {
              return (Precondition) aClass.getConstructor().newInstance();
          } catch (Exception e) {
              throw new RuntimeException(e);
          }
      }
docs: Create a new Precondition subclass based on the given tag name.