[css-anchor-position] Rephrase comment to be more explicit. w3c#8191

Author: tabatkins

css-anchor-position-1/Overview.bs

@@ -172,9 +172,9 @@ a particular element is an <dfn>implicit anchor element</dfn>
 for a given positioned element.
 
 <p class=example>
-	TODO fill in new popover-related details.
-	This makes the declared element the [=implicit anchor element=]
-	for the element with the attribute.
+	TODO: Fill in an example using the "anchor" attribute
+	(once that finally lands in the HTML spec),
+	which sets the implicit anchor element.
 
 [=Implicit anchor elements=] can be referenced
 with the ''implicit'' keyword,