[css-color-4] fix #4477 CIE L* uses a percentage

Author: svgeesus

css-color-4/Overview.bs

@@ -1685,13 +1685,16 @@ Device-independent Colors: Lab and LCH
 	CIE L*a*b*, because that is what people write in practice -->
 
 	Lab is a rectangular coordinate system with a central Lightness axis.
-	L=0 is deep black (no light at all)
-	while L=100 is a diffuse white
+	This value is usually written as a unitless number;
+	for compatibility with the rest of CSS, it is written as a percentage.
+	100% means an L value of 100, not 1.0.
+	L=0% is deep black (no light at all)
+	while L=100% is a diffuse white
 	(the illuminant is D50 white, a standardized daylight spectrum with a color temperature of 5000K,
 	as reflected by a perfect diffuse reflector).
 	Values greater than 100 would correspond to specular highlights,
 	but their precise color is undefined in this specification.
-	Usefully, L=50 is mid gray, by design,
+	Usefully, L=50% is mid gray, by design,
 	and equal increments in L are evenly spaced visually:
 	the Lab color space is intended to be perceptually uniform.
 	The a and b axes convey hue;
@@ -1715,54 +1718,52 @@ Device-independent Colors: Lab and LCH
 	is the industry standard chromatic adaptation transform,
 	and is easy to calculate as it is a simple matrix multiplication.
 
+	LCH has the same L axis as Lab,
+	but uses polar coordinates C (chroma) and H (hue).
+	C is the geometric distance from the L axis
+	and H is the angle from the positive a axis,
+	with positive angles being more clockwise.
 
-	In Lab if two colors have the same L value,
+	In Lab and LCH, if two colors have the same L value,
 	they appear to have the same visual lightness--
 	regardless of how different their hues are.
-	This is different from HSL,
-	where for example blue (#00F) and yellow (#FF0) have the same HSL lightness
-	despite yellow being obviously far lighter than blue.
 
 	
 
-	LCH has the same L axis as Lab,
-	but uses polar coordinates C (chroma) and H (hue).
-	C is the geometric distance from the L axis
-	and H is the angle from the positive a axis,
-	with positive angles being more clockwise.
-
-	Note: The Lightness axis in Lab should not be confused with the L axis in HSL.
+	Note: The Lightness axis in Lab and LCH should not be confused with the L axis in HSL.
 	For example, in HSL, the sRGB colors blue (#00F) and yellow (#FF0)
 	have the same value of L even though visually, blue is much darker.
 	In Lab, if two colors have the same measured L value,
 	they have identical visual lightness.
 	HSL and related polar RGB models were developed
+	in an attempt
 	to give similar usability benefits for RGB that LCH gave to Lab.
 
 
 
 
-Specifying Lab and LCH: the lab() and lch() functional notations
+Specifying Lab and LCH: the ''lab()'' and ''lch()'' functional notations
 	
 
 	CSS allows colors to be directly expressed in Lab and LCH.
 
 	
-	lab() = lab( <<number>> <> <> [ / <> ]? )
+	lab() = lab( <<percentage>> <> <> [ / <> ]? )
 	
 
 	The first argument specifies the CIE Lightness.
-	This is typically a number between ''0''
+	This is typically a number between ''0%''
 	(representing black)
-	and ''100''
+	and ''100%''
 	(representing white),
-	similar to the lightness argument of ''hsl()''.
+	
 	However, CIE Lightness can exceed this range on some systems,
 	with extra-bright whites using a lightness up to ''400''.
-	Values less than ''0'' must be clamped to ''0'' at computed-value time;
+	Values less than ''0%'' must be clamped to ''0%'' at computed-value time;
 	values greater than
-	''100'' are permitted (for forwards compatibility with High Dynamic Range (HDR),
+	''100%'' are permitted (for forwards compatibility with High Dynamic Range (HDR),
 	and must not be clamped.
 
 	The second and third arguments are the distances along the "a" and "b" axises
@@ -1778,7 +1779,7 @@ Specifying Lab and LCH: the lab() and lch() functional notations
 	and interpreted identically to the <> in ''rgb()''.
 
 	
-	lch() = lch( <<number>> <> <> [ / <> ]? )
+	lch() = lch( <<percentage>> <> <> [ / <> ]? )
 	
 
 	The first argument specifies the CIE Lightness,
@@ -1792,13 +1793,14 @@ Specifying Lab and LCH: the lab() and lch() functional notations
 	If the provided value is negative,
 	it is clamped to ''0'' at computed-value time.
 
-	The third argument is the hue.
-	It's interpreted identically to the <> argument of ''hsl()'',
-	but doesn't map hues to angles in the same way.
-	Instead, ''0deg'' points along the positive "a" axis (toward red),
-	''90deg'' points along the positive "b" axis (toward yellow),
-	''180deg'' points along the negative "a" axis (toward green),
-	and ''270deg'' points along the negative "b" axis (toward blue).
+	The third argument is the hue angle.
+	It's interpreted similarly to the <> argument of ''hsl()'',
+	but doesn't map hues to angles in the same way
+	because they are evenly spaced perceptually.
+	Instead, ''0deg'' points along the positive "a" axis (toward purplish red),
+	''90deg'' points along the positive "b" axis (toward mustard yellow),
+	''180deg'' points along the negative "a" axis (toward greenish cyan),
+	and ''270deg'' points along the negative "b" axis (toward sky blue).
 	If the provided value is negative,
 	or is greater than or equal to ''360deg'',
 	it is set to the value modulo 360.