[css-color-4] remove color() fallback. Fix #5931

Author: svgeesus

css-color-4/Overview.bs

@@ -3094,7 +3094,6 @@ Profiled, Device-dependent Colors</h2>
 		In each case, the numerical parameters
 		are in the range 0.0 to 1.0
 		(rather than, for example, 0 to 255).
-		<!-- add examples with alpha, and with fallback -->
 		<pre class="lang-css">
 			color: color(--swopc 0.0134 0.8078 0.7451 0.3019);
 			color: color(--indigo 0.0941 0.6274 0.3372 0.1647 0 0.0706 0.1216);
@@ -3124,19 +3123,17 @@ Profiled, Device-dependent Colors</h2>
 	Its syntax is:
 
 	<pre class='prod'>
-		<dfn>color()</dfn> = color( [ [<<ident>> | <<dashed-ident>>] [ <<number-percentage>>+ ] [ / <<alpha-value>> ]? ]# , <<color>>? )
+		<dfn>color()</dfn> = color( [<<ident>> | <<dashed-ident>>] [ <<number-percentage>>+ ] [ / <<alpha-value>> ]? )
 	</pre>
 
+	<!-- check this test, remove any fallback testing -->
 	<wpt>
 		color-function-parsing.html
 	</wpt>
 
-	The color function takes one or more comma-separated arguments,
-	with each argument specifying a color,
-	and later colors acting as "fallback" if an earlier color [=can't be displayed=]
-	(for example, if the colorspace it specifies hasn't been loaded yet).
+	The color function takes parameters specifying a color, in an explicitly listed colorspace.
 
-	Each argument represents either an <dfn export>invalid color</dfn>, as described below,
+	It represents either an <dfn export>invalid color</dfn>, as described below,
 	or a [=valid color=].
 
 	Any color which is not an [=invalid color=] is a <dfn export>valid color</dfn>.
@@ -3158,7 +3155,7 @@ Profiled, Device-dependent Colors</h2>
 	Each [=valid color=] is either in-gamut for the output device (screen, or printer),
 	or it is [=out of gamut=].
 
-	Each argument has the following form:
+	The parameters have the following form:
 
 	* An <<ident>>  or <<dashed-ident>> denoting the colorspace.
 		If this is an <<ident>> it denotes one of the <a href="#predefined">predefined colorspaces</a>
@@ -3218,40 +3215,31 @@ Profiled, Device-dependent Colors</h2>
 		This is interpreted the same way as the <<alpha-value>> in ''rgb()'',
 		and if omitted it defaults to ''100%''.
 
-	After one or more arguments of the above form,
-	a final <<color>> argument
-	using any CSS color syntax
-	can be provided.
 
+	<!--
+		remove this from wpt
 	<wpt>
 		predefined-015.html
-	</wpt>
+	</wpt> -->
 
-	This final argument can again be either a [=valid color=]
-	or an [=invalid color=]; and if valid it can be either
-	in-gamut for the output device, or [=out of gamut=].
 
 	A color which is either an [=invalid color=] or
 	an [=out of  gamut=] color
 	<dfn export>can't be displayed</dfn>.
 
-	The first choice for the value of  the ''color()'' function
-	is that it represents the color
-	specified by the first of its arguments that
-	<dfn export>can be displayed</dfn>,
-	(that is, the first argument that isn't an [=invalid color=]
-	and isn't [=out of gamut=]).
-
-	If all of its arguments [=can't be displayed=]],
-	second choice  for the value of the ''color()'' function
-	is that it represents the color
-	specified by the first of its arguments that represent
-	a [=valid color=], which will then be
+	If the specified color <dfn export>can be displayed</dfn>,
+	(that is, it isn't an [=invalid color=]
+	and isn't [=out of gamut=])
+	then this is the used value of the ''color()'' function.
+
+	If the specified color
+	is a [=valid color=]
+	but [=can't be displayed=]],
+	the used value is derived from the specified color,
 	<a>gamut-mapped</a> for display.
 
-	If all of its arguments are [=invalid color=]s,
-	the third choice for the value of the ''color()'' function
-	is that it represents <a>opaque black</a>.
+	If the color is an [=invalid color=],
+	the used value is <a>opaque black</a>.
 
 
 	<div class="example" id="ex-2020-oog-p3">
@@ -3274,34 +3262,11 @@ Profiled, Device-dependent Colors</h2>
 		produced automatically by gamut mapping.
 	</div>
 
-	<div class="example" id="ex-2020-fallback">
-		The same color as the previous example is now specified with a fallback
-		<pre class="lang-css">color(rec2020 0.42053 0.979780 0.00579, color(display-p3(0 1 0)));</pre>
-		On a display-p3 screen,
-		because the first-choice color can't be displayed
-		and because a fallback has been given which is in-gamut for the display,
-		the fallback color will be used.
-	</div>
-
-	<div class="example" id="ex-prophoto-two-fallbacks">
-		An intense green is provided in prophoto-rgb space.
-		It has a first fallback, which is the same color in display-p3
-		in case prophoto is unsupported. The color is in gamut of display-p3.
-		Lastly, a desaturated sRGB fallback is provided
-		(desaturated, as the original color is outside the sRGB gamut).
-		<pre class="lang-css">color(prophoto-rgb 0.4835 0.9167 0.2188, color(display-p3 0.3499 0.9800 0.1399, rgb(33.44% 96.68% 21.07%)))</pre>
-	</div>
-
 	<div class="invalid example" id="ex-profoto-bad">
-		Same as the previous example, but with a typo!
+		This example has a typo!
 		An intense green is provided in profoto-rgb space (which doesn't exist).
-		Ths makes it invalid, so we go to the first fallback, which is the same color in display-p3.
-		The color is in gamut of display-p3.
-		Lastly, a desaturated sRGB fallback is provided.
-		If the output device is limited to sRGB gamut,
-		the display-p3 value will be <em>out of output gamut</em>
-		so the desaturated, sRGB value is used.
-		<pre class="lang-css">color(profoto-rgb 0.4835 0.9167 0.2188, color(display-p3 0.3499 0.9800 0.1399, rgb(33.44% 96.68% 21.07%)))</pre>
+		This makes it invalid, so the used value is <a>opaque black</a>
+		<pre class="lang-css">color(profoto-rgb 0.4835 0.9167 0.2188)</pre>
 	</div>
 
 <h3 id="predefined">
@@ -3995,14 +3960,17 @@ can proceed as normal.
 </div>
 
 Fallback colors can be specified,
-for example if the specified CMYK color is known
+for example using media queries,
+to be used
+if the specified CMYK color is known
 to be outside the sRGB gamut.
 
 <div class="example" id="ex-fogra39-fallback-mq">
 	This example uses the same FOGRA39 setup as before,
 	but specifies a bright green which is outside the sRGB gamut.
 	It is, however, inside the display-p3 gamut.
 	Therefore it is displayed as-is on wide gamut screens
+	and in print,
 	and a less intense fallback color is used on sRGB screens.
 
 	<!--
@@ -4016,7 +3984,7 @@ to be outside the sRGB gamut.
 	<pre class="lang-css">
 		@media (color-gamut: srgb) {
 			.header {
-				background-color:  color(--fogra39 90% 0% 90% 0%, <span class="swatch" style="--color: rgb(8.154% 60.9704% 37.184%)"></span> rgb(8.154% 60.9704% 37.184%));
+				background-color:  rgb(8.154% 60.9704% 37.184%);
 				}
 		}
 		@media print, (color-gamut: p3){
@@ -4037,11 +4005,10 @@ to be outside the sRGB gamut.
 	Reducing the chroma until the result is in gamut
 	gives lch(56.596645% 51 154.5533771086801)
 	which is rgb(8.154% 60.9704% 37.184%)
-	and this is used as the fallback color.
+	and this has been manually specified as a fallback color.
 
 	For wide gamut screens, the color is inside the display-p3 gamut
-	so no fallback need be specified.
-	However, for the curious, the color is display-p3(0.1658 0.6147 0.3533).
+	(it is display-p3(0.1658 0.6147 0.3533) ).
 
 	<!--
 grn=[56.596645, -58.995875, 28.072154 ]