Re: Comments on Content Transformation Guidelines?

Hello Dennis

Thanks very much for your comments.

I appreciate the careful balance you draw between the advantages and 
disadvantages of content transformation.

On the specific subject of user control of the content transformation 
process, this is of crucial importance to my mind and is a strong theme 
throughout the document - though as a result of your comments we will 
need to consider whether that theme needs more careful or precise 

In detail, the task force spent a long time looking at session and 
enduring user preferences and did in fact specifically include normative 
language. We decided for various reasons to remove that section 
following a restructuring of the document. From my point of view this 
was justified partly because of the difficulty in specifying the meaning 
of "session" and "enduring" preferences, and partly because how a 
transforming proxy deals with user preferences can be legitimately 
considered to be part of product differentiation.

That said, the following sections of the document (below) refer 
specifically to this issue. My view is that we need to look at whether 
these sections hang together as a proper indication of our intent.

Thanks again for your comments, which will get entered into the tracking 
system, and against which you will receive a formal acknowledgement and 


Statements Concerning User Preferences

1.4 Summary of Requirements

      5 The Content Transformation proxy needs to be able to interact 
with the user:
          1. to allow the user to disable its features;
          2. to alert the user to the fact that it has transformed 
content and to allow access to an untransformed representation of the 

4.1.5 Alteration of HTTP Header Values

Other than to comply with transparent HTTP operation, proxies should not 
modify request headers unless:

    1. ...
    2. the user has specifically requested a restructured desktop 
experience; User Selection of Restructured Experience

Proxies may offer users an option to choose to view a restructured 
experience even when a Web site offers a choice of user experience. If a 
user has made such a choice then proxies may alter header values when 
requesting resources in order to reflect that choice, but must, on 
receipt of an indication from a Web site that it offers alternative 
representations (see Indication of Intended Presentation Media 
Type of Representation), inform the user of that and allow them to 
select an alternative representation.

Proxies should assume that by default users will wish to receive a 
representation prepared by the Web site. Proxies must assess whether a 
user's expressed preference for a restructured representation is still 
valid if a Web site changes its choice of representations (see 4.3.4 
Receipt of Vary HTTP Header). Alteration of Response


If a proxy alters the response then:

    1. ...
    2. ...
    3. It should indicate to the user that the content has been 
transformed for mobile presentation and provide an option to view the 
original, unmodified content.

E Administrative Arrangements (Non-Normative)

It is noted that there are means which fall outside of the scope of this 
document for establishing user preferences with content transformation 
proxies. It is anticipated that proxies will maintain preferences on a 
user by user and Web site by Web site basis, and will change their 
behavior in the light of changing circumstances as discussed under 4.3.4 
Receipt of Vary HTTP Header.

On 27/08/2008 18:29, Dennis Bournique wrote:
> My name is Dennis Bournique. I write about mobile browsing, primarily from a user perspective, at  I've done a little web development, mostly mobile specific sites, but I'm by no means an expert on the technical side of this issue.
> Putting on my user hat, I'd like to make a request that the Content Transformation Guidelines include a requirement that content transformation proxies "must" provide end users (consumers of web content) with a way to turn off transformation both globally and on a site by site basis.
> As an end user, I’ve experienced both the joys and the frustrations of using content transformation proxies.
> In general, I believe in content transformation as a valuable tool to make web content, which would otherwise be difficult or impossible to use, available through the limited browsers of many mobile phones.
> I have also been frustrated when a carrier or content provider unilaterally imposes content transformation with no way for me to disable it. I've been unable to access content through content transformation proxies that was previously available on the same device using a direct connection. This has happened both with installable content such as midlets and ringtones and also with pure html and xhtml pages, including mobile optimized pages and those that are not.  I have also seen my secure end to end HTTPS traffic being forced through content transformation proxies, exposing it to the potential for a "man in the middle" attack.
> I understand that the Guidelines are intended to prevent these sorts of problems by specifying when content transformation proxies must allow content to flow directly between server and user agent without modification. This is good, but no technical solution can ever be perfect.  There will always be edge cases where content transformation does more harm than good. For this reason it is important that end users have the option to opt-out of content transformation.  
> I propose that the Guidelines be amended to include the following or similar language.
> "...1. Content transformation proxies, if they are modifying traffic between a server and a user agent in any way, MUST provide a mechanism allowing the end user to resubmit the request and disable content transformation for the duration of the current session."
> "...2. Content transformation proxies, must provide a means for end users of that proxy to disable all content transformation until they take explicit action to re-enable it."

Received on Thursday, 28 August 2008 08:40:38 UTC