[css-ruby] More details about ruby-align

Author: frivoal

css-ruby-1/Overview.bs

@@ -1210,6 +1210,9 @@ Ruby Text Distribution: the 'ruby-align' property</h3>
 	Note that space distributed by 'ruby-align' is unrelated to, and independent of,
 	any space distributed due to justification.
 
+	Note: It is the content within the boxes that is aligned in the excess space,
+	not the boxes themselves.
+
 	Values have the following meanings:
 	<dl dfn-for=ruby-align dfn-type=value>
 		<dt><dfn>start</dfn></dt>
@@ -1292,16 +1295,26 @@ Ruby Text Distribution: the 'ruby-align' property</h3>
 		The distribution of space can be further controlled via 'text-justify'. [[CSS-TEXT-3]]
 	</div>
 
-	Issue: Add a paragraph explaining how to distribute space in situations with [=spanning annotations=].
-
-<!--
-	For a complex ruby with spanning elements, one additional consideration is
-	required. If the spanning element spans multiple 'rows' (other rbc or rtc
-	elements), and the ruby alignment requires space distribution among the
-	'spanned' elements, a ratio must be determined among the 'columns' of spanned
-	elements. This ratio is computed by taking into consideration the widest
-	element within each column.
--->
+	Content in [=ruby bases=] and [=ruby annotations=],
+	except those that span due to ''ruby-merge: merge'',
+	is aligned within its box based on the value of 'ruby-align' on that box.
+	Content in [=merged annotations=]
+	is aligned within the [=ruby annotation container=]
+	based on the value of 'ruby-align' on the [=annotations container=],
+	ignoring the value of 'ruby-align' on the individual [=ruby annotations=].
+
+	Issue: What if a [=merged annotation=] causes the [=ruby segment=] to be wider?
+	Does it cause each base to grow as if it were spanning them, as currently specified?
+	This does not allow e.g. centering the text in a multi-base base container
+	when its merged annotation is longer.
+	Instead, maybe we should allow ruby-merge to apply to base containers as well,
+	but this would require us either to allow a single base to span multiple annotations
+	(if the base is merged but some annotation levels are not),
+	or to require that if the base is merged, then all annotation levels must be merged as well.
+
+	The way content is aligned when 'ruby-merge' is ''ruby-merge/auto'' is up to the User Agent,
+	but must be identical to that of ''ruby-merge: separate''
+	when all annotations fit over their respective bases.
 
 <h3 id="ruby-text-decoration">
 Ruby Text Decoration</h3>