code: public Elements getElementsByTag(String tagName) {
          Validate.notEmpty(tagName);
          tagName = normalize(tagName);
  
          return Collector.collect(new Evaluator.Tag(tagName), this);
      }
docs: Finds elements, including and recursively under this element, with the specified tag name.
  @param tagName The tag name to search for (case insensitively).
  @return a matching unmodifiable list of elements. Will be empty if this element and none of its children match.