The basic idea is this: You want to be informed whenever a change (mutation) on a element or its child elements occurs. A change can be a modification of an element’s attributes, its text or if there was a child node appended or removed.

Would you have any clue what an Observable is good for, just from its name? Ok, you can observe something and the ending ‘-able’ might tell you that it lazily waits for you to be observed. Right! But how? By whom? When and why?