Re: Shadow DOM: Hat and Cat -- if that's your real name.

On Feb 4, 2014, at 6:47 PM, Tab Atkins Jr. <>

> On Tue, Feb 4, 2014 at 6:35 PM, Sylvain Galineau <> wrote:
>> On Feb 4, 2014, at 5:33 PM, Edward O'Connor <> wrote:
>>> Tab wrote:
>>>> We've just figured out that, in the general case, we need full
>>>> shadow-piercing. We'd like to explore more restricted methods of
>>>> piercing that people can opt into in the future.
>>> I think this is backwards. We should start with an opt-in mechanism and
>>> allow authors to opt-in their entire shadow tree if they really want
>>> that.
>> I would add that if Google does believe fast adoption will make some changes effectively impossible then there is no reason to expect ^^/::shadow's default level of access to the shadow tree to be any easier to change later on (defaulting to a loose model and changing to a strict one later is rarely a good time). Fast adoption makes 'fixing it later' way more expensive across the board, not just for syntax.
> We don't expect to change the default level of encapsulation, but
> rather to allow components to opt into more restrictive barriers that
> are harder to pierce.  The reason we're going for an easily-pierceable
> barrier now is that it gets us out of the way of component authors, so
> they can do their thing and innovate as they wish first.  Then we can
> come along later and figure out what more restrictive methods would
> work well.

The issue is that you're not getting in the way of anyone deliberately hacking into components. Is there data suggesting deliberate styling of custom widgets is scarce?

> If we try to be more restrictive *first*, it's extremely likely that
> we'll get things wrong, and people will have to hack around our silly
> limitations to achieve what they want.  I'd rather base the
> restrictive models on data from actual usage than guesses about what's
> good enough.  (And internal feedback from the Polymer team on our
> previous attempts at more restrictive models shows that it's very easy
> to get it wrong.)

There is some gap between 'we may get it wrong' and 'nothing at all'. I agree there is significant risk in over-thinking it; we can see some of that on this very thread: "An attribute won't do, what if people want to expose most elements in their shadow tree?'. Well, maybe a lowly attribute is a fine escape hatch to start with before moving on to more elaborate solutions derived from real-world feedback? 

So while I sympathize with your concern, my fear of picking a default we'll sorely regret later overrides it. I'd rather go the other way and start with full encapsulation; then validate various options to relax the model based on the real-world experience. 

>> Choosing the right default here seems a rather fundamental issue that deserves wide consensus before shipping anywhere. I'd love to hear more from Google on how they intend to justify the current default to would-be component developers given that, as Roc pointed out, CSS access to custom components' internals is the default today and the whole point of shadow DOM was to fix that. Is the assumption that 'shadow nodes will never match existing selectors, only new ones with the ^^ combinator' represents 'enough' encapsulation 'for now'?
> Yes.  This already puts us in a far better position than the jQuery
> status quo, where it's easy to accidentally spray the internals of a
> component with your page styles.  It's impossible for the page to
> touch a component's insides unless the page is doing so *on purpose*.
> That's already a huge win in terms of compartmentalization.

Fair point; accidental styling is eliminated. And maybe one could say 'well, people who deliberately ^^ into widgets are asking for it'. Except we can't really say that about the default behavior of a feature. So yes, it's a win, and a necessary one. I don't think it's sufficient though. 

Received on Wednesday, 5 February 2014 04:09:00 UTC