[css-ruby] Auto-hide entire annotation segment when ruby-merge is collapse.

Author: fantasai

css-ruby/Overview.bs

@@ -571,6 +571,12 @@ Autohiding Base-identical Annotations</h3>
 		</div>
 	</div>
 
+	<p>When the computed value of 'ruby-merge' is ''collapse'',
+	then all annotations and bases for that segment are compared
+	(rather than just each annotation and its base individually)
+	and the annotation for the entire segment
+	is either hidden or shown as appropriate.
+
 	<p>The content comparison for this auto-hiding behavior
 	takes place prior to white space collapsing ('white-space') and text transformation ('text-transform')
 	and ignores elements (considers only the <code>textContent</code> of the boxes).

css-ruby/Overview.html

@@ -1060,6 +1060,13 @@ <h3 class="heading settled" data-level="2.4" id="autohide"><span class="secno">2
    </div>
 
 
+   <p>When the computed value of <a class="property" data-link-type="propdesc" href="#propdef-ruby-merge">ruby-merge</a> is <a class="css" data-link-type="maybe" href="#valdef-ruby-merge-collapse">collapse</a>,
+	then all annotations and bases for that segment are compared
+	(rather than just each annotation and its base individually)
+	and the annotation for the entire segment
+	is either hidden or shown as appropriate.
+
+	</p>
    <p>The content comparison for this auto-hiding behavior
 	takes place prior to white space collapsing (<a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-text-3/#propdef-white-space">white-space</a>) and text transformation (<a class="property" data-link-type="propdesc" href="http://dev.w3.org/csswg/css-text-3/#propdef-text-transform">text-transform</a>)
 	and ignores elements (considers only the <code>textContent</code> of the boxes).