[css-text-4] Add percentages to letter-spacing and word-spacing. #2165

Author: fantasai

css-text-4/Overview.bs

@@ -7220,12 +7220,12 @@ Word Spacing: the 'word-spacing' property</h3>
 
 	<pre class="propdef">
 	Name: word-spacing
-	Value: normal | <<length>>
+	Value: normal | <<length-percentage>>
 	Initial: normal
 	Applies to: text
 	Inherited: yes
-	Percentages: N/A
-	Computed value: an absolute length
+	Percentages: relative to computed 'font-size', i.e. ''1em''
+	Computed value: an absolute length and/or a percentage
 	Animation type: by computed value type
 	Canonical order: n/a
 	</pre>
@@ -7277,12 +7277,21 @@ Word Spacing: the 'word-spacing' property</h3>
 			word-spacing-100.xht
 			</wpt>
 
-		<dt><dfn>&lt;length&gt;</dfn>
+		<dt><dfn>&lt;length-percentages&gt;</dfn>
 		<dd>
 			Specifies extra spacing
 			<em>in addition to</em> the intrinsic inter-word spacing
 			defined by the font.
 
+			Note: Percentages inherit intact,
+			and are resolved against
+			the computed 'font-size' of the current element
+			(and thus represent a size relative to
+			the size of the text to which they apply),
+			unlike ''em'' units which are resolved against
+			the computed 'font-size' of the element from which they inherit,
+			as an absolute length.
+
 			<wpt>
 			tab-size/tab-size-spacing-001.html
 			</wpt>
@@ -7400,11 +7409,12 @@ Tracking: the 'letter-spacing' property</h3>
 
 	<pre class="propdef">
 	Name: letter-spacing
-	Value: normal | <<length>>
+	Value: normal | <<length-percentage>>
 	Initial: normal
 	Applies to: <a>inline boxes</a> and text
 	Inherited: yes
-	Computed value: an absolute length
+	Percentages: relative to computed 'font-size', i.e. ''1em''
+	Computed value: an absolute length and/or a percentage
 	Animation type: by computed value type
 	Canonical order: n/a
 	</pre>
@@ -7510,6 +7520,15 @@ Tracking: the 'letter-spacing' property</h3>
 			Values may be negative,
 			but there may be implementation-dependent limits.
 
+			Note: Percentages inherit intact,
+			and are resolved against
+			the computed 'font-size' of the current element
+			(and thus represent a size relative to
+			the size of the text to which they apply),
+			unlike ''em'' units which are resolved against
+			the computed 'font-size' of the element from which they inherit,
+			as an absolute length.
+
 			<wpt>
 			tab-size/tab-size-spacing-001.html
 			</wpt>
@@ -10137,7 +10156,9 @@ Changes</h2>
 	Significant since the <a href="https://www.w3.org/TR/2019/WD-css-text-4-20191113/">2019 Working Draft</a> publication include:
 	<ul>
 		<li>Integrating the full text of [[CSS-TEXT-3]].
-		<li>
+		<li>Adding percentages to 'word-spacing' and 'letter-spacing'
+			to represent sizes relative to the current 'font-size'.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/2165">Issue 2165</a>)
 	</ul>
 
 <h3 class="no-num" id="changes-L3">