[css-ruby-1] Define ruby-overhang: auto | none per #4492

Author: fantasai

css-ruby-1/Overview.bs

@@ -556,7 +556,7 @@ Autohiding Base-identical Annotations</h3>
 
 	When the computed value of 'ruby-merge' is ''collapse'',
 	the autohiding is disabled.
-	When the computed value of 'ruby-merge' is ''auto'',
+	When the computed value of 'ruby-merge' is ''ruby-merge/auto'',
 	the user agent may decide whether to autohide or not,
 	but it is recommended to autohide if the algorithm the user agent chose
 	produces the results similar to ''separate'' would produce.
@@ -1201,14 +1201,39 @@ Edge Effects</h2>
 <h3 id="ruby-overhang">
 Overhanging Ruby</h3>
 
-	When [=ruby annotation box=] is longer than its corresponding [=ruby base box=],
-	the [=ruby annotation box=] may partially overhang adjacent boxes.
+	<pre class="propdef">
+	Name: ruby-overhang
+	Value: auto | none
+	Initial: auto
+	Applies to: ruby annotation containers
+	Inherited: yes
+	Computed value: specified keyword
+	Animation type: by computed value type
+	</pre>
+
+	The 'ruby-overhang' property controls whether [=ruby annotations=]
+	may overlap adjacent text outside the [=ruby container=].
+	Values have the following meanings:
+
+	<dl dfn-type=value dfn-for=ruby-overhang>
+		<dt><dfn>auto</dfn>
+		<dd>
+			When a [=ruby annotation container=] is longer than
+			its corresponding [=ruby base container=],
+			the [=ruby annotation container=] may 
+			partially overlap adjacent boxes.
 
-	This level of the specification does not define
-	how much the overhang may be allowed, and under what conditions.
+			Whether, how much, and under which conditions to overhang
+			are determined by the UA.
 
-	If the ruby text is not allowed to overhang,
-	then the ruby behaves like a traditional inline box,
+		<dt><dfn>none</dfn>
+		<dd>
+			A [=ruby annotation container=] is never allowed
+			to extend past the [=ruby annotation container=].
+	</dl>
+
+	When [=ruby annotations=] are not allowed to overhang,
+	the ruby behaves like a traditional inline box,
 	i.e. only its own contents are rendered within its boundaries
 	and adjacent elements do not cross the box boundary:
 
@@ -1218,33 +1243,32 @@ Overhanging Ruby</h3>
 		<p class="caption">Simple ruby whose text is not allowed to overhang adjacent text
 	</div>
 
-	However, if [=ruby annotation=] content is allowed to overhang adjacent elements
+	However, if a [=ruby annotation container=] is allowed
+	to overhang adjacent content
 	and it happens to be wider than its base,
-	then the adjacent content is partially rendered within the area of the [=ruby container box=],
-	while the [=ruby annotation=] may partially overlap the upper blank parts of the adjacent content:
+	then adjacent inline-level content
+	is partially rendered within the area of the [=ruby container box=],
+	allowing the [=ruby annotation=] to partially overlap
+	the upper/lower areas of such adjacent content:
 
 	<div class="figure">
 		<img src="images/ro-a.gif"
 		     alt="Diagram showing the ruby boxes interacting with adjacent text">
 		<p class="caption">Simple ruby whose text is allowed to overhang adjacent text
 	</div>
 
-	The [=ruby annotations=] related to a [=ruby base=]
-	must never overhang another [=ruby base=].
+	Note: Whether [=ruby annotations=] related to a [=ruby base=]
+	can overhang another [=ruby base=] is controlled by 'ruby-merge'.
 
 	The alignment of the contents of the base or the ruby text
 	is not affected by overhanging behavior.
-	The alignment is achieved the same way regardless of the overhang behavior setting
+	Alignment is achieved the same way regardless of the overhang behavior setting
 	and it is computed before the space available for overlap is determined.
 	It is controlled by the 'ruby-align' property.
 
 	Issue: I suspect overhanging interacts with alignment in some cases;
 	might need to look into this later.
 
-	This entire logic applies the same way in vertical ideographic layout,
-	only the dimension in which it works in such a layout is vertical,
-	instead of horizontal.
-
 	<div class="example">
 		The user agent may use [[JIS4051]] recommendation of
 		using one ruby text character length as the maximum overhang length.