[css-variables] Add issue about interaction of 'all' and custom props.

Author: tabatkins

css-variables/Overview.html

@@ -163,6 +163,11 @@ <h2 id="introduction" data-level="1"><span class="secno">1 </span>
 		like <span data-autolink="maybe" class="css">var-foo: var(foo);</span>,
 		but you can't get <span data-autolink="maybe" class="css">default</span> behavior.
 
+	</p><p class="issue">
+		What's the relationship of custom properties and the <a data-autolink="property" class="property" title="all">all</a> property?
+		Does it reset all the variables?
+		If <span data-autolink="maybe" class="css">var-foo: initial;</span> isn't interpreted by CSS,
+		what effect does <span data-autolink="maybe" class="css">all: initial;</span> have?
 
 </p><p>	A <dfn id="custom-property">custom property</dfn> is any property
 	whose name starts with "var-",

css-variables/Overview.src.html

@@ -92,6 +92,11 @@ <h2 id='defining-variables'>
 		like ''var-foo: var(foo);'',
 		but you can't get ''default'' behavior.
 
+	<p class='issue'>
+		What's the relationship of custom properties and the 'all' property?
+		Does it reset all the variables?
+		If ''var-foo: initial;'' isn't interpreted by CSS,
+		what effect does ''all: initial;'' have?
 
 	A <dfn>custom property</dfn> is any property
 	whose name starts with "var-",