Earlier, I said the following:
No matter what settings you set your browser to, my web page will never have the same content of the New York Time's page...
Obviously, a special browser can be written that will show my homepage identically to the way it shows the New York Time's page. That does not negate my assertion, because such a browser is no longer an independent browser; it must be getting those New York Times concrete parts from somewhere, be it through accessing the New York Times website "behind the scenes" or through storing parts of the New York Times website in its own files. Either way, the important thing is that those parts are still not coming from my web site.
From this, we can derive an important rule of thumb: In general, a renderer should be independent of its content. This is how our intuition measures whether a given browser is "honestly" rendering a site. Considering that a renderer such as a web browser can stand between its user and thousands of other people, it is very important that the browser function independently, so the user is clearly aware of who is sending the messages.
Is this an abstract consideration? Of course not. While large scale manipulation by a browser manufacturer remains a hypothetical, a small-scale demonstration of the possibilities was provided by Opera in February, 2003 with the release of the "Bork" edition of their Opera browser. From their press release:
Two weeks ago it was revealed that Microsoft's MSN portal targeted Opera users, by purposely providing them with a broken page. As a reply to MSN's treatment of its users, Opera Software today released a very special Bork edition of its Opera 7 for Windows browser. The Bork edition behaves differently on one Web site: MSN. Users accessing the MSN site will see the page transformed into the language of the famous Swedish Chef from the Muppet Show: Bork, Bork, Bork!...
"Hergee berger snooger bork," says Mary Lambert, product line manager desktop, Opera Software. "This is a joke. However, we are trying to make an important point. The MSN site is sending Opera users what appear to be intentionally distorted pages. The Bork edition illustrates how browsers could also distort content, as the Bork edition does. The real point here is that the success of the Web depends on software and Web site developers behaving well and rising above corporate rivalry."
Or, in terms of this analysis, the success of the Web depends on web browsers remaining independent of web content. Opera's "Bork" edition functions by containing a special message internally that is executed only on the MSN site, which adds content to the site that does not exist on MSN servers. While this is a largely harmless release, made to underscore a point, it demonstrates that browsers have a great deal of power over the content they are rendering. This standard of "Independence" provides a usable metric to determine whether they are wielding that power responsibly or not.