Enabling offline application storage in webkit based cocoa app

Question

What is required to enable offline web app caching for apps using the WebKit class to load web pages?

Right now, if I attempt to load the app cache like so:

cache = window.applicationCache

I get:

DOMApplicationCache
oncached: null
onchecking: null
ondownloading: null
onerror: null
onnoupdate: null
onobsolete: null
onprogress: null
onupdateready: null
status: 0

Status 0 indicates that the app is not cached. I'm thinking I just need to enable this, or perhaps set the cache path. Any ideas?