[css-color-5] hue interpolation with NaN w3c#5309

Author: svgeesus

css-color-5/Overview.bs

@@ -829,6 +829,13 @@ One way to do this is <code><i>θ</i> = ((<i>θ</i> % 360) + 360) % 360</code>.
 
 Unless otherwise specified, if no specific hue interpolation algorithm is selected by the host syntax, the default is ''shorter''.
 
+If one of the angles has the value NaN,
+then for interpolation, NaN is replaced
+by the value of the other hue angle.
+If both angles have the value NaN,
+then for interpolation, NaN is replaced
+by the value 0 for both angles.
+
 Issue(5277): How do these work when interpolating between multiple colors?
 
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