code: public void addAttr(HtmlAttr attrName, String attrValue) {
          if (attrs.isEmpty())
              attrs = new LinkedHashMap<HtmlAttr,String>(3);
          attrs.put(nullCheck(attrName), escapeHtmlChars(attrValue));
      }
docs: Adds an attribute for the HTML tag.
  
  @param attrName name of the attribute
  @param attrValue value of the attribute