Call out that <wpt> path prefixes can be overridden, and do so in the…

… example to make it clearer.

docs/index.bs

@@ -1478,7 +1478,8 @@ There are several additional optional keys:
 		You can set a different `crossorigin` value manually on the element,
 		or skip the element entirely by putting `nocrossorigin` on it or an ancestor.
 	* <dfn>WPT Path Prefix</dfn> is a partial URL path
-		that specifies a common path prefix for all of the tests in your <{wpt}> elements.
+		that specifies a default path prefix for all of the tests in your <{wpt}> elements.
+		(This can be overridden on an individual <{wpt}> element.)
 	* <dfn>WPT Display</dfn> takes the values "none", "closed", "open", or "inline",
 		and specifies whether and how <{wpt}> elements display anything in the output document.
 	* <dfn>Tracking Vector Class</dfn> is the HTML `class` attribute value used on the link inserted in elements annotated with the `tracking-vector` attribute.
@@ -3882,6 +3883,17 @@ and will override the metadata if specified.
 			no-foo-when-no-bar.html
 		</wpt>
 	</xmp>
+
+	Alternately, the path prefix could be indicated just on the one block:
+
+	<xmp highlight=html>
+		Implementations must FOO whenever they would also BAR.
+
+		<wpt pathprefix="/foo-spec/">
+			foo-whenever-you-bar.html
+			no-foo-when-no-bar.html
+		</wpt>
+	</xmp>
 </div>
 
 For debugging purposes,