[contacts] HTML Contact Sharing

I've uploaded a new proposal that defines HTML enhancements to provide
access to a user's address book data. The first draft can be viewed here:

  http://dev.w3.org/2009/dap/contacts/HTML.html

This draft is up for discussion - it does not assume consensus on the
material at this point.

The proposal is based on HTML Device [1] and reuses the basic security and
privacy principles and existing low-level parts of the programmatic Contacts
API [2] to provide address book data to a web application.

We chose to build atop of the device element for a number of reasons,
primarily because:

- unknown/unimplemented HTML input elements degrade to a text field which
isn't an intuitive user experience if the feature is not supported in the
user's current browser.

- the HTML device element is not a form-based element. That isn't the
primary intention of it's use to obtain contact information. Having said
that ...

- the HTML device element's data attribute can be serialized quite nicely
(in a JSON.stringify like manner) for transmission via web forms if it
needed to be and then deserialized (in a JSON.parse like manner) at the
other end as required. Whether the device element could/should provide
serialization guidelines is a matter for the WHATWG to decide in [1]. (in
the HTML Contact Sharing spec a note has been added to this effect). For
example, the device element's value attribute could be set to the
stringified value of the data attribute to allow for standard web form
submission and parsing on the server-side.

This proposal is an early draft and will be developed going forward.

The intention is for both the programmatic model in [2] and the HTML-based
model to co-exist within a conforming user agent, allowing a web developer
to choose the most suitable mechanism according to their application's needs
and to allow either model to function with the aid of a common user
interface/experience, contact storage and format.

All feedback is welcome and will be taken onboard in order to create the
most compelling integration model we can. As always,

- Rich

[1] http://dev.w3.org/html5/html-device/

[2] http://dev.w3.org/2009/dap/contacts/Overview.html