code: function startTag(tag, attr) {
      let attrStr = "";
      if (attr) {
          attrStr = " " + Object.keys(attr).map(function(k) { 
              return k + ' = "' + attr[k] + '"';
          }).join(" ");
      }
      return "<" + tag + attrStr + ">";
  }
docs: Returns the HTML for a start tag