[css-values-4] Simplify the computed value section, broadening it to all math function and removing some now-incorrect/irrelevant info.

Author: tabatkins

css-values-4/Overview.bs

@@ -3488,11 +3488,12 @@ Simplification</h4>
 <h3 id='calc-computed-value'>
 Computed Value</h3>
 
-	The computed value of a ''calc()'' function is the expression
-	with all components computed.
-	The computed value of a ''min()'', ''max()'', or ''clamp()'' function
-	is the comma-separated list of expressions,
-	with each expression having all its component computed.
+	The [=computed value=] of a [=math function=]
+	is its [=calculation tree=] [=simplified=],
+	using all the information available at [=computed-value=] time.
+	(Such as the ''em'' to ''px'' ratio,
+	how to resolve percentages in some properties,
+	etc.)
 
 	Where percentages are not resolved at computed-value time,
 	they are not resolved in [=math functions=],
@@ -3502,23 +3503,6 @@ Computed Value</h3>
 	(e.g. <a href="https://www.w3.org/TR/CSS21/visudet.html#the-height-property">the <css>height</css> property</a>),
 	they apply whenever a [=math function=] contains percentages.
 
-	<div class=note>
-		Note: The serialization rules do not preserve the structure of the computation,
-		so implementations can simplify the expressions
-		further than what is required here
-		when storing the values internally;
-		in particular, all [=calculation=] expressions can be reduced
-		to a sum of a <<number>>, a <<percentage>>, and some <<dimension>>s,
-		eliminating all multiplication or division,
-		and combining terms with identical units.
-
-		At this time, all units can be absolutized
-		to a single unit per type at computed-value time,
-		so at that point the [=calculation=] can be reduced
-		to just a <<number>>, a <<percentage>>, and a single absolute <<dimension>> of the appropriate type,
-		per expression.
-	</div>
-
 	<div class='example'>
 		For example,
 		whereas 'font-size' computes percentage values at <a>computed value</a> time
@@ -3530,11 +3514,6 @@ Computed Value</h3>
 		whereas 'font-size' will compute such expressions directly into a length.
 	</div>
 
-	<!-- http://lists.w3.org/Archives/Public/www-style/2010May/0001.html
-	This has notes on how we should handle things when calc() is extended to
-	handle unit mult/div. Related to this is <unit>mod<unit>, which can return
-	0 and thus introduce computed-time division-by-zero. -->
-
 	Given the complexities of width and height calculations on table cells and table elements,
 	math expressions mixing both percentages and lengths for widths and heights on
 	table columns, table column groups, table rows, table row groups, and table cells