What is the difference between screenX/Y, clientX/Y and pageX/Y?

Question

What is the difference between screenX/Y, clientX/Y and pageX/Y?

Also for iPad Safari,

Answer 1

The difference between those will depend largely on what browser you are currently referring to. Each one implements these properties differently, or not at all. Quirksmode has great documentation regarding browser differences in regards to W3C standards like the DOM and JavaScript Events.