ParentNode interface isn't implemented in lib.d.ts

[LPGhatguy]

The ParentNode interface, as defined by MDN, includes properties like children and firstElementChild, implemented by Element, Document, and DocumentFragment.

Here's the documentation for ParentNode.children: https://developer.mozilla.org/en-US/docs/Web/API/ParentNode/children

It's marked as 'experimental' but is implemented in all mainstream browsers (all Chrome, FF 3.5+, IE 9+)

I've tested this with TypeScript 1.5.3 (via the ST plugin's language services) and the latest 1.6-dev.