[whatwg] Proposal to extend registerProtocolHandler

[timeless]

If offering a potentially registerable api is done via
<link rel="protocol-handler" type="foopy:" href="...">

Then it'd be reasonable for a handling page to return some well known
HTTP response (410?) to indicate that the API is no longer supported.

The site wouldn't need to call a method, and the user agent would be
able to do something reasonable *when* the user cared about the
problem.

For the case where the site wants the user to change from an old
(dying) api to a new api, the site could use some other well known
HTTP response (301?).

And yes, it seems perfectly reasonable for UAs to collect possible
handlers and let the user choose one when the user needs to use one.
-- This is, for example, more or less how Windows handles removable
media or other forms of content. And it matches more or less how UAs
handle RSS feeds and search engines...