code: public Builder end() {
          if (ends.isEmpty())
              throw new IllegalStateException("No pending tag/section to close.");
          String tag = ends.pop();
          html.a(tag);
          if (newLineAfterTheseTags.contains(tag.toLowerCase())) {
              html.nl();
              text.nl();
          }
          return this;
      }
docs: Closes the last opened tag or section.
  
  @return this builder
  @throws IllegalStateException if there are no pending tags to close