new Abstract.TimedObserver(element, frequency, callback)

• element (String | Element) – The DOM element to watch. Can be an element instance or an ID.
• frequency (Number) – The frequency, in seconds — e.g., 0.33 to check for changes every third of a second.
• callback (Function) – The callback to trigger when the value changes.

Initializes an Abstract.TimedObserver; used by subclasses.