Re: [webcomponents] [Custom Elements] the `extends` property cannot be replaced (#326)

Hi @bkardell , I know it has been a long discussion, yet you didn't tell me *why is that a problem* concretely, this part I miss.

You've also commented the "extra content" second example more than the main issue I've initially reported: table rows, cells, captions.

I wrote it's not as compelling use case as table rows or cells because a wrap might just do, yet I dont understand any of your points. Methods? If it's not recognized as Custom Element due browser limitations there's nothing to worry about, it's an image.

`width` and `height` ? Already used and styled without problems. You are basically saying there are issues in something that has no issue at all and already works in prod even on IE8.

Regardless, once again, that is not the main issue: LI, TR, TD, COL, CAPTION, other elements outside their parent context *are* the issue so let's focus on these cases ;-)

If we have "some element can be extended, some other can't" the API will fail in consistency, and developer expectations will be compromised like shown in the `x-tr` example.

> in your final example it does seem to me you could use the wrapper approach 

Please provide an example of custom TR that works in a regular table (simply because of its peculiar layout that works like that since the beginning of the time), otherwise I don't see how any wrapper could work.

The only way I see this solvable without `extend` and `is` is improving specifications in a way that if the inherited object is "one of those special cases" then it should be accepted as exception whenever it's supposed to be accepted (a `tbody` element in this case)  without ever loosing it's ability to be populated via `innerHTML` like its inherited counterpart would do.

Let's remember that this works already since ever:
```js
var tr  = document.createElement('tr');
tr.innerHTML = '<td>yes, it works as easy as this</td>';
```
And let's think  on  why on earth something  that extends that `tr


---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/326#issuecomment-142323935