=== Type of Data ===
Flags:
* things the user enters, except for credentials (form data)
* credentials
* things cached by the UA (pages, preview images, icons)
* local data stored by the server / web application (cookies, HTML5 local storage, Flash/Silverlight local storage)
* history information (bookmarks, visited URIs)
* settings specific to a site (for instance, preferences with respect to privacy, script disabling...)
Several UAs offer to restrict the clear operation to a time range such as "today" or "last week".
In the API, this can be exposed as "last N minutes", or something like that.
We need to allow plugins to signal that they can't clear by time range, though.
(Return code, plus discoverability beforehand?)
=== Site/URI ===