Sean Hogan wrote:
What is the reason for the native implementation requirement? Is it W3C policy?
There's a couple of reasons for this. The main reason being that JavaScript libraries are not limited by the same compatibility constraints as a browser, and so something that could be implemented in a JavaScript library without any problems may prove to have backwards compatibility issues with some legacy sites and affect a browser's ability to implement it. Basically, in this sense, a JS library is effectively a walled garden implementation where it's only used on sites that are explicitly built for it. So allowing such implementations to count effectively undermines the whole purpose of the implementation requirement, which is there to help demonstrate that the spec works in practice.
The other reason is that it's not always technically possible for a JS library to implement all the required functionality due to the limitations of the DOM, or at least some implementations of it. For example, it's not possible in IE to add the methods to the prototypes for the Document, Element or DocumentFragment nodes. Also, in practice, implementations like in JQuery don't actually try to implement the methods themselves. They just implement somewhat compatible functionality and expose it on their own objects (e.g. $("div>p"); instead of document.querySelector("div>p");).
-- Lachlan Hunt - Opera Software http://lachy.id.au/ http://www.opera.com/
