[css-color-5] Recover text defining adjusters that was removed from color-mix and move it to color-adjust

Author: LeaVerou

css-color-5/Overview.bs

@@ -555,9 +555,47 @@ Adjusting colors: the ''color-adjust'' function {#coloradjust}
 	Multiple color functions can be specified.
 
 	<pre class='prod'>
-		<dfn>color-adjust()</dfn> = color-adjust( <<color>> [ color-adjuster [ in <<colorspace>> ]? ]? )
+		<dfn>color-adjust()</dfn> = color-adjust( <<color>> [ <<color-adjuster>> && [ in <<colorspace>> ]? ]? )
 	</pre>
 
+	<pre class='prod'>
+		<dfn>&lt;color-adjuster></dfn> = [ [
+				  <<srgb-adjuster>> | <<hsl-adjuster>> | <<hwb-adjuster>>
+				| <<xyz-adjuster>> | <<lab-adjuster>> | <<lch-adjuster>>
+			] | alpha ] <<percentage>>?
+		<dfn>&lt;srgb-adjuster></dfn> = red || green || blue
+		<dfn>&lt;hsl-adjuster></dfn> = <<hue-adjuster>> || saturation || lightness
+		<dfn>&lt;hwb-adjuster></dfn> = <<hue-adjuster>> ||  whiteness || blackness
+		<dfn>&lt;xyz-adjuster></dfn> = x || y || z
+		<dfn>&lt;lab-adjuster></dfn> = lightness || a || b
+		<dfn>&lt;lch-adjuster></dfn> = lightness || chroma || <<hue-adjuster>>
+		<dfn>&lt;hue-adjuster></dfn> = hue [shorter | longer | increasing | decreasing | specified ]?
+	</pre>
+
+	The meaning of the adjusters is defined by colorspace.
+	For example, if the [=colorspace=] is [=hsl=],
+	hue means the HSL hue, which is not the same as the LCH hue;
+	if the colorspace is [=lch=],
+	lightness means the LCH Lightness, which is the same as Lab lightness,
+	but different to the HSL Lightness.
+
+	Only the [=color-adjuster=]s defined for a given [=colorspace=] are available.
+	For example, it is not possible to use the HWB [=whiteness=] adjuster unless the colorspace is [=hwb=].
+	The alpha adjuster is available on any [=colorspace=].
+
+	Note: not all [=color-adjuster=]s are equally useful.
+	Adjustments in LCH are the most useful, which is why it is the default.
+	Adjustments on the a and b axes are rarely needed.
+	Adjustments in the srgb-related spaces (srgb itself, hsl, hwb)
+	are provided mainly for backward compatibility
+	with the sorts of adjustments currently done in CSS preprocessors.
+	Adjusting the individual x, y and z channels will produce significant hue shifts;
+	however, adjusting all three channels together is useful
+	and will lighten or darken the color.
+
+	The [=hue-adjuster=] takes optional keywords, to specify the [[css-color-4#hue-interpolation]] algorithm.
+	If no keyword is specified, it is as if ''shorter'' were specified.
+
 	<div class="example">
 		This example produces the adjustment of peru (#CD853F),
 		in ''lch()'' colorspace (the default),