[css-color-hdr] Update dynamic-range-limit-mix to reflect #10271.

css-color-hdr/Overview.bs

@@ -257,12 +257,12 @@ The 'dynamic-range-limit' property {#the-dynamic-range-limit-property}
 
 	<pre class='propdef'>
 		Name: dynamic-range-limit
-		Value: standard | high | constrained-high
+		Value: standard | high | constrained-high | ''dynamic-range-limit-mix()''
 		Initial: high
 		Applies to: all elements
 		Inherited: no
 		Percentages: n/a
-		Computed value: specified value
+		Computed value: see <a href="#computing-dynamic-range-limit">Computed Value for 'dynamic-range-limit'</a>
 		Animation type: by ''dynamic-range-limit-mix()'' 
 		Canonical order: per grammar
 	</pre>
@@ -309,10 +309,49 @@ Mixing Dynamic Range Limits: the ''dynamic-range-limit-mix()'' function {#dynami
 
 
 <pre class='prod'>
-	<dfn>dynamic-range-limit-mix()</dfn> = dynamic-range-limit-mix( [ <<ident>> && <<percentage [0,100]>>? ]#{2})
+	<dfn>dynamic-range-limit-mix()</dfn> = dynamic-range-limit-mix( [ <<ident>> && <<percentage [0,100]>> ]+)
 </pre>
 
-	Percentages are normalized in the same way as ''color-mix()''.
+  If the sum of all percentages is 0%, then the function is invalid.
+
+<h3 id="computing-dynamic-range-limit">
+  Computed Value for 'dynamic-range-limit'
+</h3>
+
+  If the specified value is ''standard'', ''constrained-high'', or ''high'', then the computed value is the specified value.
+
+  If the specified value is ''dynamic-range-limit-mix()'', then the computed value is determined by the following algorithm:
+
+  1. Let <var>v1</var>, ..., <var>vN</var> be the computed values for the parameters to be mixed.
+  2. Let <var>p1</var>, ..., <var>pN</var> be the mixing percentages, normalized to sum to 100%.
+  3. Define the contributing percentages as:
+     * Let <var>p1_standard</var>,...,<var>pN_standard</var> be the percentages for ''standard'' in <var>v1</var>,...,<var>vN</var>
+     * Let <var>p1_constrained_high</var>,...,<var>pN_constrained_high</var> be the percentages for ''constrained-high'' in <var>v1</var>,...,<var>vN</var>
+     * Let <var>p1_high</var>,...,<var>pN_high</var> be the percentages for ''high'' in <var>v1</var>,...,<var>vN</var>
+  4. Compute the weighted sums as:
+     * <var>p_standard</var>=(<var>p1_standard</var>*<var>p1</var>+...+<var>pN_standard</var>*<var>pN</var>)/100.
+     * <var>p_constrained_high</var>=(<var>p1_constrained_high</var>*<var>p1</var>+...+<var>pN_constrained_high</var>*<var>pN</var>)/100.
+     * <var>p_high</var>=(<var>p1_high</var>*<var>p1</var>+...+<var>pN_high</var>*<var>pN</var>)/100.
+  5. If <var>p_standard</var>, <var>p_constrained_high</var>, or <var>p_high</var> equals 100%, then
+     the computed value is ''standard'', ''constrained-high'', or ''high'', respectively.
+  6. Otherwise, the computed value is ''dynamic-range-limit-mix()'', with parameters
+     ''standard'', ''constrained-high'', and ''high'', in that order, and percentages
+     <var>p_standard</var>, <var>p_constrained_high</var>, and <var>p_high</var>,
+     omitting parameters with a percentage equal to 0%.
+
+	<div class="example" id="ex-hdr-limit-mix">
+		The computed value of
+	  <pre class="lang-css">
+    dynamic-range-limit-mix(
+        high 10%,
+        dynamic-range-limit-mix(standard 25%, constrained-high 75%) 20%,
+        dynamic-range-limit-mix(constrained-high 10%, high 30%) 20%)
+    </pre>
+    is
+	  <pre class="lang-css">
+        dynamic-range-limit-mix(standard 10%, constrained-high 40%, high 50%)
+    </pre>
+	</div>
 
 <h2 id="color-function">
 	Specifying Predefined and Custom Color Spaces: the ''color()'' Function