One additional point, unrelated to accessibility: "is" also enables piggybacking to special parser behavior of existing elements. For example, I can extend <template> or <link>.
Here are some examples: http://jsbin.com/xuheb/3/edit?html,output https://blog.polymer-project.org/howto/2014/09/11/template-is-autobinding/ :DG< On Thu, Jan 29, 2015 at 7:33 AM, Bruce Lawson <bru...@opera.com> wrote: > On 29 January 2015 at 14:54, Steve Faulkner <faulkner.st...@gmail.com> > wrote: > > I think being able to extend existing elements has potential value to > > developers far beyond accessibility (it just so happens that > accessibility > > is helped a lot by re-use of existing HTML features.) > > I agree with everything Steve has said about accessibility. Extending > existing elements also gives us progressive enhancement potential. > > Try https://rawgit.com/alice/web-components-demos/master/index.html in > Safari or IE. The second column isn't functional because it's using > brand new custom elements. The first column loses the web componenty > sparkles but remains functional because it extends existing HTML > elements. > > There's a similar story with Opera Mini, which is used by at least > 250m people (and another potential 100m transitioning on Microsoft > feature phones) because of its proxy architecture. > > Like Steve, I've no particularly affection (or enmity) towards the > <input type="radio" is="luscious-radio"> syntax. But I'd like to know, > if it's dropped, how progressive enhancement can be achieved so we > don't lock out users of browsers that don't have web components > capabilities, JavaScript disabled or proxy browsers. If there is a > concrete plan, please point me to it. If there isn't, it's > irresponsible to drop a method that we can see working in the example > above with nothing else to replace it. > > I also have a niggling worry that this may affect the uptake of web > components. When I led a dev team for a large UK legal site, there's > absolutely no way we could have used a technology that was > non-functional in older/proxy browsers. > > bruce > >