Don't use parentElement

When you try to access the parent element of a specific HTML element in the DOM, make sure you are using a standard parentNode property of the element. parentElement is an IE specific definition of parentNode. IE supports parentNode but FF, whose version is lower than 10, does not support parentElement.

As far as I understand Microsoft wanted to add parentElement in addition to standard parentNode in order to keep the naming convention with other function calls. (e.g. createElement)