[css-values-5] Revert previous edit about simplification at specified/computed time, it's just an interpolation operation.

Author: tabatkins

css-values-5/Overview.bs

@@ -3679,49 +3679,39 @@ calc-size/interpolate-size-parsing.html
 <h3 id=resolving-calc-size>
 Resolving ''calc-size()''</h3>
 
-	The value of a ''calc-size()''
-	is resolved first by [=calc-size()/simplifying=] it
-	as described below in [[#simplifying-calc-size]].
+	Before [=used value=] time,
+	''calc-size()'' functions are not resolved or simplified.
+	(But see [[#interpolate-calc-size]].)
 
-	Then, at used-value time,
+	At [=used value=] time,
 	the [=calc-size calculation=] is resolved
-	just like the value of a ''calc()'' expression
+	just like the value of a ''calc()'' expression,
 	by substituting in the used value of the [=calc-size basis=]
 	for the ''calc-size()/size'' keyword in the [=calc-size calculation=],
 	and evaluating any percentages normally (if they are [=definite=])
 	or against ''0px'' (if they are not).
 
-	Note: If the [=calc-size basis=] is ''calc-size()/any'',
-	the ''calc-size()'' resolves exactly as a [=definite=] length
-	equal to its [=calc-size calculation=].
-
-	Note: A percentage in the [=calc-size basis=]
-	is treated differently:
-	[[#simplifying-calc-size|simplification]]
-	moves the percentage into the [=calc-size calculation=]
-	and replaces it with ''size'' references.
-	The [=calc-size basis=] then becomes ''100%'',
-	behaving as whatever ''100%'' would normally do in that context,
-	including possibly making a property [=behave as auto=], etc.
-
 	<div class=note>
-		Percentages in the basis work as normal
+		Percentages in the [=calc-size basis=] resolve as normal
 		so you can always smoothly transition to <em>any</em> size,
 		regardless of its value or behavior.
-		For example, without ''calc-size()'',
-		transitioning from ''100%'' to ''0px''
-		only works smoothly if the percentage is [=definite=];
-		if it's not, then during the entire transition
-		the property might [=behave as auto=]
-		and not actually change size at all.
-
-		Percentages in the calculation, on the other hand,
-		are resolved to 0 when indefinite
+		For example, ''calc-size(100%, size)''
+		is guaranteed to interpolate smoothly with ''calc-size(100%, 0px)'',
+		producing intermediate values like ''calc-size(100%, size * .5)''.
+		Without ''calc-size()'',
+		interpolation from ''100%'' to ''0px'' only works as expected
+		if the percentage is [=definite=];
+		otherwise, the intermediate values like ''calc(50%)''
+		might all [=behave as auto=]
+		and not change size at all.
+
+		Percentages in the [=calc-size calculation=], on the other hand,
+		are resolved to ''0px'' when they would otherwise be indefinite,
 		to avoid making the ''calc-size()''
-		potentially act in two different ways;
-		there are some cases where a ''width/min-content'' size
+		potentially act in two different ways.
+		There are some cases where a ''width/min-content'' size, for example,
 		will cause different layout effects than a ''100%'' size,
-		and so a ''calc-size()'' has to masquerade as one or the other.
+		and so a ''calc-size()'' has to commit to one behavior or the other.
 	</div>
 
 
@@ -3751,10 +3741,10 @@ calc-size/animation/interpolate-size-width-interpolation.html
 
 	Whether two ''calc-size()'' functions can be interpolated
 	depends on their [=calc-size basis=] values
-	(after being [=calc-size()/simplified=]):
+	(after being [=calc-size()/simplified for interpolation=]):
 
 	<dl class=switch>
-		: If either function returned failure from being [=calc-size()/simplified=]
+		: If either function returned failure from being [=calc-size()/simplified for interpolation=]
 		:: The values cannot be interpolated.
 
 		: If they are identical
@@ -3833,15 +3823,18 @@ calc-size/animation/interpolate-size-width-interpolation.html
 <h4 id=simplifying-calc-size>
 Simplifying ''calc-size()''</h4>
 
-	Similar to [=math functions=],
-	at both [=specified value=] and [=computed value=] times
-	the [=calc-size calculation=]
-	(and the [=calc-size basis=], if it's a <<calc-sum>>)
-	are simplified to the extent possible,
-	as follows:
+	Before [=interpolation=],
+	''calc-size()'' functions are [=calc-size()/simplified for interpolation=]
+	so their [=calc-size basises=] can be compared,
+	and their [=calc-size calculations=] can be interpolated properly.
+
+	Note: Unlike [=math functions=],
+	this simplification is <em>not</em> done at other times.
+	The simplification can fail due to substitution exploding,
+	similar to [[#long-substitution]].
 
 	<div algorithm>
-		To <dfn for=calc-size()>simplify</dfn>
+		To <dfn for=calc-size()>simplify for interpolation</dfn>
 		a ''calc-size()'' function:
 
 		<ol>
@@ -3875,14 +3868,12 @@ Simplifying ''calc-size()''</h4>
 				returns failure,
 				the entire operation immediately returns failure.
 
-				ISSUE: And then what?
-
 			<li>
 				Next, simplify the [=calc-size calculation=]
 				as defined in [[css-values-4#calc-simplification]].
 		</ol>
 
-		Note: After canonicalization,
+		Note: After simplification,
 		the [=calc-size basis=] of a ''calc-size()'' function
 		will either be a single keyword or the value ''100%''.
 	</div>