[css-text-decor-4] Clean up intro

Author: fantasai

css-text-decor-4/Overview.bs

@@ -36,23 +36,24 @@ Introduction</h2>
 	CSS Levels 1 and 2 only defined very basic <a href="#line-decoration">line decorations</a>
 	(underlines, overlines, and strike-throughs)
 	appropriate to Western typographical traditions.
-	Level 3 of this module adds the ability to change
+	Level 3 of this module added the ability to change
 	the color, style, position, and continuity of these decorations,
-	and also introduces
+	and also introduced
 	<a href="#emphasis-marks">emphasis marks</a> (traditionally used in East Asian typography),
 	and <a href="#text-shadow-property">shadows</a> (which were proposed then deferred from Level 2).
+	Level 4 introduces additional controls over these decorations.
 
 <h3 id="placement">
 Module Interactions</h3>
 
 	This module replaces and extends the text-decorating
-	features defined in [[!CSS2]] chapter 16.
+	features defined in [[CSS-TEXT-DECOR-3]].
 
 <h3 id="values">
 Values</h3>
 
 	This specification follows the <a href="https://www.w3.org/TR/CSS21/about.html#property-defs">CSS property definition conventions</a> from [[!CSS2]].
-	Value types not defined in this specification are defined in CSS Values & Units [[!CSS-VALUES-3]].
+	Value types not defined in this specification are defined in CSS Values & Units [[!CSS-VALUES]].
 	Other CSS modules may expand the definitions of these value types.
 
 	In addition to the property-specific values listed in their definitions,
@@ -62,9 +63,9 @@ Values</h3>
 
 <h3 id="terms">Terminology</h3>
 
-	The terms <dfn><a href="https://www.w3.org/TR/css-text-3/#grapheme-cluster">character</a></dfn>,
-	<dfn><a href="https://www.w3.org/TR/css-text-3/#letter">letter</a></dfn>, and
-	<dfn><a href="https://www.w3.org/TR/css-text-3/#content-language">content language</a></dfn>
+	The terms [=typographic character unit=] (<dfn>character</dfn>),
+	[=typographic letter unit=] ([=letter=]),
+	and [=content language=]
 	as used in this specification are defined in [[!CSS-TEXT-3]].
 	Other terminology and concepts used in this specification are defined
 	in [[!CSS2]] and [[!CSS-WRITING-MODES-4]].
@@ -336,7 +337,7 @@ Automatic Thickness of Text Decoration Lines</h4>
 Determining the Position and Thickness of Line Decorations</h3>
 
 	Issue: This section is copied over from early drafts of Text Decoration Level 3.
-	It is still under review, and needs integration with 'text-underline-offset' and 'text-decoration-width'.
+	It is still under review, and needs integration with 'text-underline-offset' and 'text-decoration-thickness'.
 
 	Since line decorations can span elements with varying font sizes and
 	vertical alignments, the best position for a line decoration is not