function startTyping() {
                    addCaret(element);
                    totalChars = interpolateText(element[0], scope, totalChars, originalNodeValues, true);
                    window.requestAnimationFrame(tick);
                }
These two variables are used to store the original text values of any text nodes in the element. The original approach involved
simply appending a new property onto the DOM node itself, but this proved to be a bad idea since it breaks in IE. This new approach
is a little more complex since we now have to track the index of each text node in the originalNodeValues array.
@type {Array}