[css-text-4] Review-based fixups

Author: frivoal

css-text-4/Overview.bs

@@ -93,15 +93,19 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 	A <dfn data-dfn-for='' data-dfn-type=dfn>virtual word boundary</dfn> is similar to the presence
 	of the ZERO WIDTH SPACE (U+200B) character:
 	it introduces a [=soft wrap opportunity=]
-	and is affected by the 'word-boundary-expansion' property;
-	its presence has no effect on text shaping,
+	and is affected by the 'word-boundary-expansion' property.
+	Its presence has no effect on text shaping,
 	nor on 'word-spacing'.
-	However, its insertion must have no effect on the underlying content,
+	However, inserting [=virtual word boundaries=] must have no effect on the underlying content,
 	and must not affect the content of a plain text copy &amp; paste operation.
 
 	<dl dfn-type=value dfn-for=word-boundary-detection>
 		<dt><dfn>manual</dfn>
 		<dd>
+			Linguistic analysis is <em>not</em> used
+			in any language or writing system
+			to determine line wrapping opportunities not indicated by the markup or characters of the element.
+
 			The User Agent must not insert [=virtual word boundaries=].
 
 			[=Typographic character units=] with class SA in [[!UAX14]]
@@ -170,7 +174,8 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 			(see [[BCP47]]).
 			If the UA does not support word-boundary detection
 			for <em>all</em> languages represented by the specified range,
-			it must reject that value at parse-time.
+			that specified value is invalid
+			(and will cause the declaration to be ingored).
 
 			Note: Wildcards <em>in the language subtag</em> would imply
 			support for detecting word boundaries in an undefined and effectively unlimited set of languages.
@@ -197,7 +202,7 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 			with both the [=content language=] and <<lang>>
 			<i>canonicalized</i> and converted to <i>extlang form</i>
 			as per section 4.5 of [[!RFC5646]],
-			then the [=used value=] is ''word-boundary-detection/manual'',
+			then the [=used value=] is ''word-boundary-detection/normal'',
 			and this property has no effect on this element.
 			Otherwise,
 			the User Agent must insert a [=virtual word boundary=]
@@ -224,6 +229,7 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 
 	<div class=example>
 		Specifying the language for which the word boundary detection is to be performed
+		and making unsupported language ranges invalid
 		is required in order to make this feature meaningfully testable with ''@supports''.
 
 		For example, Japanese text normally allows line breaking between letters of a word
@@ -349,7 +355,7 @@ Makig Word Boundaries Visible: the 'word-boundary-expansion' property</h4>
 	</dl>
 
 	The User Agent must not replace
-	instances of U+200B imediately preceding or following
+	instances of U+200B immediately preceding or following
 	a [=forced line break=]
 	(ignoring any intervening inline box boundaries,
 	and associated 'margin'/'border'/'padding').
@@ -374,6 +380,10 @@ Makig Word Boundaries Visible: the 'word-boundary-expansion' property</h4>
 	rather than additional values to 'text-transform' because:
 	* This property needs to take effect before [[CSS-TEXT-3#white-space-rules]],
 		but 'text-transform' happens after that.
+		This is needed so that the spaces inserted by this property
+		behave as normal spaces for text layout purposes,
+		and can collapse with other collapsible spaces
+		or participate in [[css-text-3#white-space-phase-2|Trimming and Positioning]].
 	* The uses cases for this property and 'text-transform',
 		and the author's decision to apply either or both,
 		are independent,