code: public static String innerHTML(String url, String markup, String selector) {
          ensureMarkup(url, markup);
          Document document = documents.get(url);
          Elements elements = document.select(selector);
          return elements.html();
      }
docs: Retrieves the content of the matched elements, without their own markup tags, identified by the {@code selector} from the given
  {@code markup}. The {@code url} is used only for caching purposes, to avoid parsing multiple times the markup returned for the
  same resource.
  
  @param url      the url that identifies the markup
  @param markup   the markup
  @param selector the selector used for retrieval
  @return the contents of the selected element