What’s the difference between `HTMLElement` and `Element`?

An HTMLElement is an Element, as defined in the HTML extension to the DOM Level 2 Core specification:

interface HTMLElement : Element {
           attribute DOMString       id;
           attribute DOMString       title;
           attribute DOMString       lang;
           attribute DOMString       dir;
           attribute DOMString       className;
};

Element (per specification) refers to the Element interface as it is defined in the DOM Core Level 2 specification (there is also another DOM Core specification (working draft) though).

Update: There are a lot of specifications out there and it is not totally clear which browsers use which one (to me).

Maybe someone else has more insight…

But in any case, Element is a more generic interface than HTMLElement and the latter inherits from the former.

Update 2: A nice way to see the inheritance structure is to execute console.dir(elementReference) for any element (works in Chrome/Safari, needs Firebug for Firefox).