Proposal for changes to manage Shadow DOM content distribution

Hi all,

Following WebApps discussion last year [1] and earlier this year [2] about template transclusions and inheritance in shadow DOM, Jan Miksovsky at Component Kitchen, Ted O'Connor and I (Ryosuke Niwa) at Apple had a meeting where we came up with changes to the way shadow DOM distributes nodes to better fit real world use cases.

After studying various real world use of web component APIs as well as exiting GUI frameworks, we noticed that selector based node distribution as currently spec'ed doesn't address common use cases and the extra flexibility CSS selectors offers isn't needed in practice.  Instead, we propose named insertion "slots" that could be filled with the contents in the original DOM as well as contents in subclasses.  Because the proposal uses the same slot filling mechanism for content distributions and inheritance transclusions, it eliminates the need for multiple shadow roots.

Please take a look at our proposal at https://github.com/w3c/webcomponents/wiki/Proposal-for-changes-to-manage-Shadow-DOM-content-distribution <https://github.com/w3c/webcomponents/wiki/Proposal-for-changes-to-manage-Shadow-DOM-content-distribution>

[1] https://lists.w3.org/Archives/Public/public-webapps/2014AprJun/0151.html <https://lists.w3.org/Archives/Public/public-webapps/2014AprJun/0151.html>
[2] https://lists.w3.org/Archives/Public/public-webapps/2015JanMar/0611.html <https://lists.w3.org/Archives/Public/public-webapps/2015JanMar/0611.html>