[css-images-4][editorial] Improve introductory text for <color-interpolation-method>

Author: fantasai

css-images-4/Overview.bs

@@ -1191,18 +1191,26 @@ Gradients</h2>
 Linear Gradients: the ''linear-gradient()'' notation {#linear-gradients}
 ------------------------------------------------------------------------
 
-Compared to [[css3-images]], this level adds a <<color-interpolation-method>> token
-to customize color interpolation in gradients as described in [[css-color-4#interpolation]].
+	This level adds a <<color-interpolation-method>> argument
+	to ''linear-gradient()'' and ''repeating-linear-gradient()'',
+	indicating the color space and path to use
+	when interpolating colors on the gradient line.
+	See [[css-color-4#interpolation]].
 
-<pre class=prod>
+	<pre class=prod>
 		<dfn>linear-gradient()</dfn> = linear-gradient(
 			[ <<angle>> | to <<side-or-corner>> ]? || <<color-interpolation-method>>,
 			<<color-stop-list>>
 		)
 		<dfn>&lt;side-or-corner></dfn> = [left | right] || [top | bottom]
 	</pre>
 
-The effect of colorspace on interpolation can be marked.
+<h4 id="color-interpolation">
+Effects of color space on interpolation: examples</h4>
+
+	<p><em>This section is non-normative.</em>
+
+The effect of colorspace on interpolation can be significant.
 
 <div class="example">
 	In this example, a linear gradient between the same pair of colors
@@ -1330,10 +1338,13 @@ to bring them back into gamut.
 Radial Gradients: the ''radial-gradient()'' notation {#radial-gradients}
 ------------------------------------------------------------------------
 
-Compared to [[css3-images]], this level adds a <<color-interpolation-method>> token
-to customize color interpolation in gradients as described in [[css-color-4#interpolation]].
+	This level adds a <<color-interpolation-method>> argument
+	to ''radial-gradient()'' and ''repeating-radial-gradient()'',
+	indicating the color space and path to use
+	when interpolating colors on the gradient line.
+	See [[css-color-4#interpolation]].
 
-<pre class=prod>
+	<pre class=prod>
 		<dfn>radial-gradient()</dfn> = radial-gradient(
 		  [[ <<ending-shape>> || <<size>> ]? [ at <<position>> ]? ] || <<color-interpolation-method>>,
 		  <<color-stop-list>>