[css-text-decor][css-ruby] Allow UA to shift ruby/emphasis marks if they conflict with underlines/overlines. <w3c#160>

Author: fantasai

css-ruby/Overview.bs

@@ -1156,7 +1156,13 @@ Ruby Text Decoration</h3>
 	<p>Text decoration may be specified directly on ruby base containers
 	and ruby annotation containers:
 	in such cases it is propagated to all of the container's bases or annotations (respectively),
-	and is also drawn between them.
+	and is also drawn between them for continuity.
+
+	<p>The positions of ruby annotations may be adjusted to avoid conflicts
+	with overline and underline decorations applied to the base text.
+	In the basic case of consistent font size and baseline alignment,
+	an underline or overline is to be positioned
+	between the base level and any annotations on that side.
 
 	<p class="issue">This section needs some clarification about
 	drawing decorations between the content of adjacent bases/annotations.

css-text-decor/Overview.bs

@@ -768,6 +768,8 @@ Emphasis Mark Position: the 'text-emphasis-position' property</h3>
   <p>Emphasis marks are drawn exactly as if each character was
     assigned the mark as its ruby annotation text with the ruby position
     given by 'text-emphasis-position' and the ruby alignment as centered.
+    Note that this position may be adjusted if it conflicts
+    with underline or overline decorations.
 
   <p>The effect of emphasis marks on the line height is the same as for
     ruby text.</p>