[mediaqueries] Define that min/max-* is invalid in a boolean context. Matches impls.

--HG--
extra : rebase_source : b186a4e147b68df100146f23b580387b8b9b7b5e

Author: tabatkins

mediaqueries/Overview.bs

@@ -667,6 +667,9 @@ Using “min-” and “max-” Prefixes On Range Features</h4>
 		as it accepts the values ''0'' and ''1''.)
 	</div>
 
+	Attempting to evaluate a min/max prefixed <a>media feature</a> in a <a>boolean context</a>
+	is invalid and a syntax error.
+
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mediaqueries/Overview.html

@@ -1106,6 +1106,9 @@ <h4 class="heading settled" data-level=2.4.4 id=mq-min-max><span class=secno>2.4
 		as it accepts the values <span class=css>0</span> and <span class=css>1</span>.)
 	</div>
 
+<p>Attempting to evaluate a min/max prefixed <a data-link-type=dfn href=#media-feature title="media feature">media feature</a> in a <a data-link-type=dfn href=#boolean-context title="boolean context">boolean context</a>
+	is invalid and a syntax error.</p>
+
 
 
 <h2 class="heading settled" data-level=3 id=mq-syntax><span class=secno>3 </span><span class=content>