How to get offset relative to a specific parent?

Question

I want to get the offset of an element relative to a specific parent not the direct one and not the document.

I looked for that on the internet and found the of

Answer 1

you need to subtract as OffSet implies the navigator window

var offset = GetOffSet( $("#a"), $("#b") );

function GetOffSet( elem, elemParent ) {
    return elemParent.position().left - elem.parent().position().left;
}