[css-color-5] Add dashed-ident to color-interpolation method, w3c#7377

Author: svgeesus

css-color-5/Overview.bs

@@ -2306,6 +2306,38 @@ or any other color or monochrome output device which has been characterized.
 			<li>alpha is the same as the input color
 		</ul>
 
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+
+<h2 id="interpolation">
+	Color Interpolation</h2>
+
+<h3 id="interpolation-space">
+	Color Space for Interpolation</h3>
+
+	The <<color-interpolation-method>> is extended to allow use of the 
+	<a href="#custom-color">custom color spaces</a>:
+
+	<pre class='prod'>
+		<dfn export>&lt;color-space></dfn> = &lt;rectangular-color-space> | &lt;polar-color-space> | &lt; custom-color-space>
+		<dfn export>&lt;rectangular-color-space></dfn> = ''srgb'' | ''srgb-linear'' | ''lab'' | ''oklab'' | ''xyz'' | ''xyz-d50'' | ''xyz-d65''
+		<dfn export>&lt;polar-color-space></dfn> = ''hsl'' | ''hwb'' | ''lch'' | ''oklch''
+		<dfn export>&lt;custom-color-space></dfn> = <<dashed-ident>>
+		<dfn export>&lt;hue-interpolation-method></dfn> = [ shorter | longer | increasing | decreasing ] hue
+		<dfn export id="color-interpolation-method">&lt;color-interpolation-method></dfn> = in [ <<rectangular-color-space>> | <<polar-color-space>> <<hue-interpolation-method>>? | &lt; custom-color-space> ]
+	</pre>
+
+	The <<dashed-ident>> must have been declared 
+	in a valid ''@color-profile'' rule, 
+	otherwise the <<color-interpolation-method>> is invalid.
+
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