Content Transformation Addendum to Web Browsing Style Guide

If you have taken the time and trouble to create a "made for mobile" experience, the last thing you would want is that this gets altered by a third party.

We've published a consultative document that suggests ways for you to stop that happening. We suggest that by adding two existing HTTP headers to responses, content providers can make it absolutely clear what they expect content transforming proxies to do with their content. By adding these headers, transforming proxies should be in no doubt what the content provider has in mind.

We know this means extra work for developers, and that's a pain. But a small one. We think that this is a lot less work than trying to get yourself white listed by everyone concerned.

In short, we say that if you put "no-transform" in a Cache-Control header then that makes it clear to transforming proxies that they must not touch your content.

We also say to put a "Vary" header on your response. If you say "Vary: User-Agent" that makes it clear to a transforming proxy that if they have replaced the user's actual User Agent string, then the content they've received is probably not the right content.

Andrea has written an article about how to configure your server environment, or edit your php or asp scripts to do this.

We appreciate that this is a small part of the solution to a really complex issue. We know a lot of developers feel passionate about dealing with these issues – and for those content providers that have been economically affected, understandably.

We are anxious to help develop a more complete solution that addresses a whole range of issues and hopefully restore some balance to the fragile, but growing mobile ecosystem.

To that end we strongly support and are highly active in the W3C Mobile Web Best Practices Working Group, and its Content Transformation Task Force. The group plans to publish guidelines in draft form in October and for full public comment in mid-December. In the meantime the group works in public, and the Editor's drafts of the documents plus the discussion on the list are available to anyone who cares to take an interest.

Please bear in mind that the group hasn't made up its mind about any particular solution, and that contributions of the participant's opinions are made in good faith and in the spirit of exploring the options. It may be that we are strongly opposed to each other's views as initially expressed.

That said, however strongly we disagree, we have committed to finding consensus. It's not always easy to do, but it does recognise that no single point of view or special interest should prevail over others. This is an eco-system that has to work as such. We think that working in that forum is the way to achieve it.

In the meantime, please consider our recommendation that you make absolutely clear what your intentions are in respect of your content.


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