docs: public String prettyHtml() {
          StringBuilder html = new StringBuilder();
          for (Change aDiff : getChangeList()) {
              String text = aDiff.text.replace("&", "&amp;")
                                      .replace("<", "&lt;")
                                      .replace(">", "&gt;")
                                      .replace("\n", "&para;<br>");
              switch (aDiff.operation) {
                  case INSERT:
                      html.append("<ins style=\"background:#e6ffe6;\">").append(text)
                          .append("</ins>");
                      break;
                  case DELETE:
                      html.append("<del style=\"background:#ffe6e6;\">").append(text)
                          .append("</del>");
                      break;
                  case EQUAL:
                      html.append("<span>").append(text).append("</span>");
                      break;
              }
          }
          return html.toString();
      }