Add Declarative Shadow DOM (non-harmful)

Closes #335.

Author: annevk

Diff for: activities.json

@@ -361,6 +361,19 @@
     "title": "Custom elements",
     "url": "https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements"
   },
+  {
+    "ciuName": null,
+    "description": "Markup for ShadowRoot nodes.",
+    "id": "declarative-shadow-dom",
+    "mdnUrl": null,
+    "mozBugUrl": null,
+    "mozPosition": "non-harmful",
+    "mozPositionDetail": "We're not convinced that the complexity this feature introduces upon the HTML parser carries its weight in terms of usefulness for web developers. There's also a risk that the processing model is not compatible with a future declarative custom elements feature as it was developed in isolation. Having said that, the proposal is a reasonable approach for this functionality that takes into account the various constraints and security considerations that come with changing the HTML parser.",
+    "mozPositionIssue": 335,
+    "org": "Proposal",
+    "title": "Declarative Shadow DOM",
+    "url": "https://github.com/mfreed7/declarative-shadow-dom/blob/master/README.md"
+  },
   {
     "ciuName": null,
     "description": "This will allow custom elements to have \"default\" accessibility semantics, analogous to how built-in elements have \"implicit\" or \"native\" semantics.",