[css-inline-3] Some cleanup of alignment-baseline definition

Author: fantasai

css-inline-3/Overview.bs

@@ -293,7 +293,7 @@ Baseline Metrics</h3>
 	see [[#baseline-tables]] and [[#baseline-synthesis]].
 
 <h4 id="baseline-tables">
-Deriving Baselines</h4>
+Baselines of Glyphs and Boxes</h4>
 
 	Each font, glyph, and [=inline-level box=]
 	is assumed to have a [=baseline=] coordinate
@@ -304,9 +304,9 @@ Deriving Baselines</h4>
 	For an [=inline box=], it derives from its [=first available font=]
 	regardless of whether the box actually contains any glyphs from that font.
 	For [=atomic inlines=], it is the box’s alignment [=baseline set=]
-	(as chosen by 'baseline-source')
-	if any;
-	or else is synthesized from the box’s dimensions,
+	(as chosen by 'baseline-source');
+	if the box has no [=baseline set=]
+	then one is [=synthesize baseline|synthesized=] from its [=margin box=],
 	see [[#baseline-synthesis-replaced]].
 
 	Each font is assumed to have its own <dfn>baseline table</dfn>
@@ -535,12 +535,14 @@ Alignment Baseline Type: the 'alignment-baseline' longhand</h4>
 	Animation type: discrete
 	</pre>
 
-	<p>Specifies what point of an inline-level box is aligned to what point in the parent.
-	Also selects the <a>alignment baseline</a> of boxes aligned with 'align-self'/'justify-self'.
+	This property specifies the box’s <dfn export>alignment baseline</dfn>:
+	the [=baseline=] used to align the box
+	prior to applying its [=baseline shift=].
 
-	ISSUE: Clean up this prose to correctly handle alignment contexts other than inline formatting contexts.
-
-	Values are defined below:
+	The <dfn>alignment baseline values</dfn>,
+	which specify which [=baseline=] of the box is aligned
+	to the corresponding [=baseline=] of its [=alignment context=]
+	when performing [=baseline alignment=], are defined below:
 
 	<dl dfn-for=alignment-baseline dfn-type=value>
 		<dt><dfn>baseline</dfn>
@@ -580,13 +582,11 @@ Alignment Baseline Type: the 'alignment-baseline' longhand</h4>
 			Match the box’s [=text-over baseline=] to that of its parent.
 	</dl>
 
-	For the purposes of transverse alignment within a [=line box=],
-	an [=atomic inline=] that has no [=baseline sets=]
-	uses baselines [=synthesize baseline|synthesized=]
-	from its [=margin box=].
-
-	For the following definitions, the <a>alignment subtree</a>
-	is as defined in [[!CSS2]].
+	The <dfn>line-relative alignment values</dfn>,
+	which reference the [=line-over=] and [=line-under=] edges
+	of the box’s [=aligned subtree=] [[!CSS2]]
+	and align with respect to the corresponding edges of the [=line box=] itself,
+	are defined below:
 
 	<dl dfn-for=alignment-baseline dfn-type=value>
 		<dt><dfn>top</dfn>