[css-2015] Add issue markers to highlight changes.

Author: fantasai

css-2015/Overview.bs

@@ -384,6 +384,9 @@ Requirements for Responsible Implementation of CSS</h2>
 
 	<ol>
 		<li>
+
+			Issue: Rewritten per gregwhitworth's feedback.
+
 			Implementations of <a>unstable</a> features
 			that are described in W3C specifications
 			but are not interoperable
@@ -417,6 +420,9 @@ Requirements for Responsible Implementation of CSS</h2>
 			as a pre-CR spec that hasn't changed in awhile is usually more out-of-date than stable.
 
 		<li>
+
+			Issue: Added "should not" against encumbered features, per dbaron's request.
+
 			If at least three UAs implement a feature
 			(or if a browser has broken the previous rule and shipped for broad use
 			an <a>unstable</a> or otherwise non-standard feature in a production release),
@@ -444,11 +450,11 @@ Requirements for Responsible Implementation of CSS</h2>
 				particularly because details have not been ironed out through the standards review process.
 			</details>
 
-			When exposing such an <a>unstable</a> feature to the Web in a production release,
+			<p>When exposing such an <a>unstable</a> feature to the Web in a production release,
 			implementations should support both prefixed and unprefixed syntaxes
 			for the feature.
-			Once the feature has stabilized and the implementation is updated to match interoperable behavior,
-			support for the prefixed syntax should be removed.
+			<ins>Once the feature has stabilized and the implementation is updated to match interoperable behavior,
+			support for the prefixed syntax should be removed.</ins>
 
 			<details class=why>
 				<summary>Why?</summary>
@@ -458,10 +464,16 @@ Requirements for Responsible Implementation of CSS</h2>
 				as they get ironed out through the standards/bugfixing process.
 			</details>
 
-			Vendors <em>should</em> provide spec-editing and testing resources
+			<p>Vendors <em>should</em> provide spec-editing and testing resources
 			to complete standardization of such features.
+			<ins>Vendors <em>should not</em> use this clause as an excuse to release features
+			that cannot be freely implemented by their competitors
+			(due to platform dependency, licensing restrictions, etc.).</ins>
 
 		<li>
+
+			Issue: Rewritten as open vs. closed systems instead of Web vs. non-Web, per szilles' request.
+
 			A CSS feature is a <dfn>proprietary extension</dfn> if it is meant for use
 			in a closed environment accessible only to a single vendor's user agent(s).
 			A UA should support such <a>proprietary extensions</a>