[css-inline-3] Mention AAT baseline values in metrics section per Myles's request

Author: fantasai

css-inline-3/Overview.bs

@@ -352,7 +352,8 @@ Baselines and Metrics</h3>
 			corresponds to the bottom of most, but not all, their characters,
 			(such as “m”, “Ш”, “Δ”).
 			Often represented as zero in font design coordinate systems;
-			assigned <code>romn</code> in OpenType.
+			assigned to <code>romn</code> in OpenType
+			and to <code>bsln</code> value zero in TrueType AAT.
 
 		<dt><dfn lt="cap-height baseline" local-lt="cap-height">cap-height</dfn>
 		<dd>
@@ -379,42 +380,44 @@ Baselines and Metrics</h3>
 		<dd>
 			Corresponds to
 			the [=line-over=] design edge of CJK (Han/Hangul/Kana) text.
-			Assigned <code>idtp</code> in OpenType.
+			Assigned to <code>idtp</code> in OpenType.
 
 		<dt><dfn lt="ideographic-under baseline" local-lt="ideographic-under">ideographic-under</dfn>
 		<dd>
 			Corresponds to
 			the [=line-under=] design edge of CJK (Han/Hangul/Kana) text.
-			Assigned <code>ideo</code> in OpenType.
+			Assigned to <code>ideo</code> in OpenType.
 
 		<dt><dfn lt="central baseline" local-lt="central">central</dfn>
 		<dd>
 			Corresponds to the ideographic central baseline,
 			halfway between the [=ideographic-under=] and [=ideographic-over=] baselines.
+			Assigned to <code>bsln</code> value 1 in TrueType AAT.
 
 		<dt><dfn lt="ideographic-ink-over baseline" local-lt="ideographic-ink-over">ideographic-ink-over</dfn>
 		<dd>
 			Corresponds to the [=line-over=] ink edge of CJK (Han/Hangul/Kana) text.
-			Assigned <code>icft</code> in OpenType.
+			Assigned to <code>icft</code> in OpenType.
 
 		<dt><dfn lt="ideographic-ink-under baseline" local-lt="ideographic-ink-under">ideographic-ink-under</dfn>
 		<dd>
 			Corresponds to the line-under ink edge of CJK (Han/Hangul/Kana) text.
 			Assigned <code>icfb</code> in OpenType.
 
-
 		<dt><dfn lt="hanging baseline" local-lt="hanging">hanging</dfn>
 		<dd>
 			Corresponds to hanging baseline
 			from which characters in
 			Tibetan and similar unicameral scripts
 			with a strong but not absolute top edge seem to “hang”.
-			Assigned <code>hang</code> in OpenType.
+			Assigned to <code>hang</code> in OpenType
+			and to <code>bsln</code> value 3 in TrueType AAT.
 
 		<dt><dfn lt="math baseline" local-lt="math">math</dfn>
 		<dd>
 			Corresponds to center baseline around which mathematical characters are designed.
-			Assigned <code>math</code> in OpenType.
+			Assigned to <code>math</code> in OpenType
+			and <code>bsln</code> value 4 in TrueType AAT.
 
 		<dt><dfn lt="text-over baseline" local-lt="text-over">text-over</dfn>
 		<dd>