The actual state isolation is modeled by Alloy facts. The
rst fact states that each cookie in the model is tagged with
the RenderingEngine of the ScriptContext in which it was
rst received. The next states that access to cookies are
restricted to only ScriptContexts from an origin matching
the domain setting of the cookie executing in a Renderin-
gEngine matching the cookie tag.
Our app container model also includes a browser behavior
relevant to app isolation, as described by Section 6.1: it
associates a newly opened ScriptContext with the existing
RenderingEngine of an app if the top-level URL of the new
ScriptContext is within the app.
Finally, our modeling assumes that users will behave con-
servatively within an isolated app window, meaning attack-
ers cannot get their ScriptContexts in the same Renderin-
gEngine as an app when separate RenderingEngines exist.