Re: Proposal for changes to manage Shadow DOM content distribution

On Wed, Apr 22, 2015 at 2:37 PM, Ryosuke Niwa <rniwa@apple.com> wrote:

>
> On Apr 22, 2015, at 10:16 AM, Justin Fagnani <justinfagnani@google.com>
> wrote:
>
>
>
> On Tue, Apr 21, 2015 at 10:40 PM, Ryosuke Niwa <rniwa@apple.com> wrote:
>
>>
>> > On Apr 21, 2015, at 10:23 PM, Justin Fagnani <justinfagnani@google.com>
>> wrote:
>> >
>> > I do want the ability to redirect distributed nodes into a holes in the
>> base template, so that part is welcome to me. However, my first reaction to
>> the slot idea is that forcing users to add the content-slot attribute on
>> children significantly impairs the DOM API surface area of custom elements.
>> >
>> > For the single-level distribution case, how is this different from
>> <content select="[content-slot=name]"> except that content select can
>> distribute based on features of the children that might already exist, like
>> tag names or an attribute?
>>
>> At the conceptual level, they're equivalent.  However, we didn't find the
>> extra flexibility of using CSS selectors compelling as we mentioned in our
>> proposal [1].
>>
>
> I personally would like to see more power, especially positional
> selectors. Some components would be better off selecting their first child,
> rather than requiring a class.
>
>
> What are concrete use cases that require such flexibility?
>

Require is a strong word :) but the case I recently experienced was a panel
with a header. It always expects one child for the header and the rest for
content. There are several ways to do this, and one would be to select the
first child into one distribution point and the rest into another. Another
way is to use attributes, classes or a specific set of tag names. The key
for me here is that you give the custom element author a choice on how to
shape their API.



>
> [1] See points 3 and 4 in
>> https://github.com/w3c/webcomponents/wiki/Proposal-for-changes-to-manage-Shadow-DOM-content-distribution#some-issues-with-the-current-shadow-dom-spec
>
>
> Point 4 is interesting, because unless I'm missing something (which could
> be!) it's incorrect. You can create selectors with :not() that exclude the
> content selectors that come after in document order. I would rewrite the
> example as:
>
> <template>
>   <content select=".header"></content>
>   <content select=":not(.footer)"></content>
>   <content select=".footer"></content>
> </template>
>
> Our point wasn't so much that it's not achievable.  With enough hackeries
> and "techniques", we can.  The problem is the developer ergonomics of
> content element with select attribute with common real world use cases.
> For example, the above code is a lot more verbose and less intuitive than
>
> <template>
>   <content slot="header"></content>
>   <content></content>
>   <content slot="footer"></content>
> </template>
>
> This is true, but it's a trade off for custom element *authoring* brevity
vs custom element *use* brevity (and authoring expressiveness). I'd
personally rather optimize for custom element user ergonomics, and give
custom element authors the power to make their elements easy and convenient.

Continuing this example I would actually make the selectors more complex
because we have these nice semantic elements in html5:

<template>
  <content select="header, .header"></content>
  <content select=":not(footer, .footer)"></content>
  <content select="footer, .footer"></content>
</template>

 Which is more work for the CE author, but allows this for the user:

<my-element>
  <header>Title</header>
  <p>...</p>
  <p>...</p>
  <footer>...</footer>
</my-element>


Cheers,
  Justin


- R. Niwa
>
>