[css-color-4] Update grammar, trim mentions of custom colorspaces

Author: svgeesus

css-color-4/Overview.bs

@@ -3406,8 +3406,20 @@ Profiled, Device-dependent Colors</h2>
 	(rather than the implicit sRGB color space that most of the other color functions operate in).
 	Its syntax is:
 
-	<pre class='prod'>
+	<!-- <pre class='prod'>
 		<dfn>color()</dfn> = color( [<<ident>> | <<dashed-ident>>] [<<number-percentage>> | none]+ [ / [<<alpha-value>> | none] ]? )
+	</pre> -->
+
+	<!-- this one from Color 5,
+		then cut down to remove color 5-specific bits
+		like RCS and custom colors
+	-->
+	<pre class='prod'>
+		<dfn>color()</dfn> = color( <<colorspace-params>> [ / <<alpha-value>> ]? )
+		<dfn>colorspace-params</dfn> = [ <<predefined-rgb-params>> | <<xyz-params>>]
+		<dfn>predefined-rgb-params</dfn> = <<predefined-rgb>> [ <<number>> | <<percentage>> | none ]{3}
+		<dfn>predefined-rgb</dfn> = srgb | display-p3 | a98-rgb | prophoto-rgb | rec2020
+		<dfn>xyz-params</dfn> = xyz [ <<number>> | none ]{3}
 	</pre>
 
 	<!-- check this test, remove any fallback testing -->
@@ -3441,39 +3453,21 @@ Profiled, Device-dependent Colors</h2>
 
 	The parameters have the following form:
 
-	* An <<ident>>  or <<dashed-ident>> denoting the color space.
-		If this is an <<ident>> it denotes one of the <a href="#predefined">predefined color spaces</a>
-		(such as ''display-p3'');
-		if it is a <<dashed-ident>> it denotes a custom
-		color space, defined by a ''@color-profile'' rule.
+	* An <<ident>> denoting
+		one of the <a href="#predefined">predefined color spaces</a>
+		(such as ''display-p3'')
 		Individual <a href="#predefined">predefined color spaces</a>
 		may further restrict whether <<number>>s or <<percentage>>s
 		or both, may be used.
 
 		If the <<ident>> names a non-existent color space
 		(a name that does not match one of the <a href="#predefined">predefined color spaces</a>),
-		or a predefined but unsupported color space,
-		this argument represents an <a>invalid color</a>.
-
-		If the <<dashed-ident>> names a non-existent color space
-		( a name that does not match an <a>color profile's</a> name,
-		  or which matches but the corresponding profile has not loaded,
-		  or does not represent a valid profile),
 		this argument represents an <a>invalid color</a>.
 
 
 	* One or more <<number>>s or <<percentage>>s providing the parameter values that the color space takes.
 
-		For custom color spaces,
-		specified component values
-		less than 0 or 0%, or greater than 1 or 100%
-		are not invalid;
-		they are clamped to the valid range at computed value time.
-		This is because ICC profiles typically do not accept
-		out of range input values.
-
-		For predefined color spaces,
-		specified component values
+		Specified component values
 		less than 0 or 0%, or greater than 1 or 100%
 		are not invalid;
 		these out of gamut colors