docs: function(el, attrName) {
                      var oldValue;
                      if (!attr.MutationObserver) {
                          oldValue = attr.get(el, attrName);
                      }
  
                      var setter = attr.map[attrName];
                      if (typeof setter === "function") {
                          setter(el, undefined);
                      }
                      if (setter === true) {
                          el[attrName] = false;
                      } else if (typeof setter === "string") {
                          el[setter] = "";
                      } else {
                          el.removeAttribute(attrName);
                      }
                      if (!attr.MutationObserver && oldValue != null) {
                          attr.trigger(el, attrName, oldValue);
                      }
  
                  }