[css-color-4] start on color() serialization

Author: svgeesus

css-color-4/Overview.bs

@@ -747,6 +747,50 @@ This section updates and replaces that part of CSS Object Model, section
 		<p>is the string "lab(56.2% 83.51 -3.79 / 0.93)"</p>
 	</div>
 
+	<h4 id="serializing-color-values">Serializing values of the ''color()'' function</h4>
+
+	The serialized form of ''color()'' values
+	is derived from the [=computed value=]
+	and uses the ''color()'' form,
+	with lowercase letters for the function name
+	and the colorspace name.
+
+	The component values are serialized in base 10,
+	as <<number>>.
+	A single ASII space character " "
+	must be used as the separator
+	between the component values.
+
+	Trailing fractional zeroes in any component values must be omitted;
+	if the fractional part consists of all zeroes,
+	the decimal point must also be omitted.
+
+	<div class="example" id="ex-color-serial">
+		<p>The serialized value of</p>
+		<pre class="lang-css"><span class="swatch" style="--color: rgba(99.56%, 6.09%, 57.02%, 0.93)"></span> color(dIsPlAy-P3  0.964  0.763  0.787)</pre>
+		<p>Is the string "color(display-p3 0.96 0.76 0.79)",
+		if two decimal places are retained.
+		Notice that 0.787 has rounded up to 0.79,
+		rather than being truncated to 0.78.
+		</p>
+	</div>
+
+	If the colorspace is sRGB, the colorspace must be omitted in the serialized result.
+	<!--
+		could go either way on that but we need to pick one, and this is shorter
+	-->
+
+	The precision with which ''color'' component values are retained,
+	and thus the number of significant figures in the serialized value,
+	is not defined in this specification,
+	but for RGB and CMYK colorspaces must at least be sufficient
+	to round-trip values
+	with eight bit precision;
+	this will result in at least two decimal places
+	unless trailing zeroes have been omitted.
+	(16bit, or half float, is recommended for internal storage).
+	Values must be rounded, not truncated.
+
 <h2 id='numeric-srgb'>
 sRGB Colors</h2>