[css-text-decor-4] Clarify application to ::first-line and ::first-letter. Include text-emphasis-position per w3c#2998 see also w3c#4642

Author: fantasai

css-ruby-1/Overview.bs

@@ -42,7 +42,8 @@ Module interactions</h3>
 
 	<p>None of the properties in this module apply to the ''::first-line'' or
 	''::first-letter'' pseudo-elements,
-	except for 'ruby-position' which applies to ''::first-line''.
+	except for 'ruby-position' which applies to ''::first-line'',
+	inheriting to affect ruby annotations on the first line.
 
 <h3 id="values">
 Values</h3>

css-text-decor-4/Overview.bs

@@ -49,6 +49,9 @@ Module Interactions</h3>
 	This module replaces and extends the text-decorating
 	features defined in [[CSS-TEXT-DECOR-3]].
 
+	All of the properties in this module
+	can be applied to the ''::first-line'' and ''::first-letter'' [=pseudo-elements=].
+
 <h3 id="values">
 Values</h3>