code: public Elements getElementsByClass(String className) {
          Validate.notEmpty(className);
  
          return Collector.collect(new Evaluator.Class(className), this);
      }
docs: Find elements that have this class, including or under this element. Case insensitive.
  <p>
  Elements can have multiple classes (e.g. {@code <div class="header round first">}. This method
  checks each class, so you can find the above with {@code el.getElementsByClass("header");}.
  
  @param className the name of the class to search for.
  @return elements with the supplied class name, empty if none
  @see #hasClass(String)
  @see #classNames()