[css-color-4] consistent minimum precision between lab() and color(lab)

Author: svgeesus

css-color-4/Overview.bs

@@ -851,12 +851,17 @@ and there shall be no thousands separator.
 	but due to the wide gamut must be sufficient
 	to round-trip L values between 0 and 100,
 	and a and b values between ±127,
-	with at least twelve bit precision;
-	this will result in at least two decimal places
+	with at least sixteen bit precision;
+	this will result in at least three decimal places
 	unless trailing zeroes have been omitted.
-	(16bit, or half float, is recommended for internal storage).
+	(half float or float, is recommended for internal storage).
 	Values must be <a href="https://drafts.csswg.org/css-values-4/#combine-integers">rounded towards +∞</a>, not truncated.
 
+	Note: a and b values outside ±127 are possible
+	with ultrawide gamut spaces. For example, <em>all</em>
+	of the ''prophoto-rgb'' primaries and secondaries
+	exceed this range, but are within ±200.
+
 	<a href="#serializing-alpha-values">As noted earlier</a>,
 	unitary alpha values are not explicitly serialized.
 	Non-unitary alpha values must be explicitly serialized,
@@ -3498,7 +3503,7 @@ Predefined colorspaces: ''srgb'', ''display-p3'', ''a98-rgb'', ''prophoto-rgb'',
 				<figure>
 					<img src="images/prophoto-prim-sec.svg" style="width: 80.68vmin"
 					alt="diagram of rec2020 primaries and secondaries in LCH">
-					<figcaption>Visualization of the protphoto-rgb colorspace in LCH. The primaries and secondaries are shown
+					<figcaption>Visualization of the prophoto-rgb colorspace in LCH. The primaries and secondaries are shown
 					(but in sRGB, not in the correct colors).
 					For comparison, the sRGB primaries and secondaries
 					are also shown, as dashed circles.