[whatwg] a rel=attachment

[Ian Fette (イアンフェッティ)]

Many websites wish to offer a file for download, even though it could
potentially be viewed inline (take images, PDFs, or word documents as an
example). Traditionally the only way to achieve this is to set a
content-disposition header. *However, sometimes it is not possible for the
page author to have control over the response headers sent by the
server.*(A related example is offline apps, which may wish to provide
the user with
a way to "download" a file stored locally using the filesystem API but again
can't set any headers.) It would be nice to provide the page author with a
client side mechanism to trigger a download.

After mulling this over with some application developers who are trying to
use this functionality, it seems like adding a "rel" attribute to the <a>
tag would be a straightforward, minimally invasive way to address this use
case. <a rel=attachment href=blah.pdf> would indicate that the browser
should treat this link as if the response came with a content-disposition:
attachment header, and offer to download/save the file for the user.

-Ian