[css-values-4] Rephrase some trig and type bits to be more precise, and allow referring to types of calculations more easily.

Author: tabatkins

css-values-4/Overview.bs

@@ -2285,7 +2285,8 @@ Basic Arithmetic: ''calc()''</h3>
 
 	A ''calc()'' function contains a single <dfn export for="calc()">calculation</dfn>,
 	which is a sequence of values interspersed with operators,
-	and possibly grouped by parentheses,
+	and possibly grouped by parentheses
+	(matching the <<calc-sum>> grammar),
 	which represents the result of evaluating the expression
 	using standard operator precedence rules.
 	(<css>*</css> and <css>/</css> bind tighter than <css>+</css> and <css>-</css>,
@@ -2494,7 +2495,7 @@ Type Checking</h3>
 
 	A [=math function=] can be many possible types,
 	such as <<length>>, <<number>>, etc.,
-	depending on the expression it contains,
+	depending on the [=calculations=] it contains,
 	as defined below.
 	It can be used anywhere a value of that type is allowed.
 
@@ -2519,70 +2520,76 @@ Type Checking</h3>
 	and to make division-by-zero detectable at parse time.
 	This version now relaxes those restrictions.
 
-	[=Math functions=] allow arbitrary expressions,
-	so long as the expression as a whole resolves to a singular unit
-	according to the following rules:
-
-	* At a <css>+</css> or <css>-</css> sub-expression,
-		attempt to [=add two types|add the types=] of the left and right arguments.
-		If this returns failure,
-		the entire [=math function=] is invalid.
-		Otherwise, the sub-expression's [=CSSNumericValue/type=] is the returned type.
-
-	* At a <css>*</css> sub-expression,
-		[=multiply two types|multiply the types=] of the left and right arguments.
-		The sub-expression's [=CSSNumericValue/type=] is the returned result.
-
-	* At a <css>/</css> sub-expression,
-		let |left type| be the result of finding the [=CSSNumericValue/types=] of its left argument,
-		and |right type| be the result of finding the [=CSSNumericValue/types=] of its right argument
-		and then [=invert a type|inverting=] it.
-
-		The sub-expression's [=CSSNumericValue/type=] is the result of
-		[=multiply two types|multiplying=] the |left type| and |right type|.
-
-	* Anything else is a terminal value,
-		whose [=CSSNumericValue/type=] is determined based on its CSS type:
-
-		<dl class=switch>
-			: <<number>>
-			: <<integer>>
-			:: the [=CSSNumericValue/type=] is «[ ]» (empty map)
-			: <<length>>
-			:: the [=CSSNumericValue/type=] is «[ "length" → 1 ]»
-			: <<angle>>
-			:: the [=CSSNumericValue/type=] is «[ "angle" → 1 ]»
-			: <<time>>
-			:: the [=CSSNumericValue/type=] is «[ "time" → 1 ]»
-			: <<frequency>>
-			:: the [=CSSNumericValue/type=] is «[ "frequency" → 1 ]»
-			: <<resolution>>
-			:: the [=CSSNumericValue/type=] is «[ "resolution" → 1 ]»
-			: <<flex>>
-			:: the [=CSSNumericValue/type=] is «[ "flex" → 1 ]»
-			: <<percentage>>
-			::
-				If, in the context in which the [=math function=] is placed,
-				<<percentage>>s are resolved relative to another type of value
-				(such as in 'width', where <<percentage>> is resolved against a <<length>>),
-				and that other type is <em>not</em> <<number>>,
-				the [=CSSNumericValue/type=] is determined as the other type.
-
-				Otherwise,
-				the [=CSSNumericValue/type=] is «[ "percent" → 1 ]».
-			: anything else
-			:: The [=math function=] is invalid.
-		</dl>
-
-		In all cases, the associated [=percent hint=] is null.
+	<div algorithm>
+		To <dfn>determine the type of a [=calculation=]</dfn>:
+
+		* At a <css>+</css> or <css>-</css> sub-expression,
+			attempt to [=add two types|add the types=] of the left and right arguments.
+			If this returns failure,
+			the entire [=calculation’s=] type is failure.
+			Otherwise, the sub-expression's [=CSSNumericValue/type=] is the returned type.
+
+		* At a <css>*</css> sub-expression,
+			[=multiply two types|multiply the types=] of the left and right arguments.
+			The sub-expression's [=CSSNumericValue/type=] is the returned result.
+
+		* At a <css>/</css> sub-expression,
+			let |left type| be the result of finding the [=CSSNumericValue/types=] of its left argument,
+			and |right type| be the result of finding the [=CSSNumericValue/types=] of its right argument
+			and then [=invert a type|inverting=] it.
+
+			The sub-expression's [=CSSNumericValue/type=] is the result of
+			[=multiply two types|multiplying=] the |left type| and |right type|.
+
+		* Anything else is a terminal value,
+			whose [=CSSNumericValue/type=] is determined based on its CSS type:
+
+			<dl class=switch>
+				: <<number>>
+				: <<integer>>
+				:: the [=CSSNumericValue/type=] is «[ ]» (empty map)
+				: <<length>>
+				:: the [=CSSNumericValue/type=] is «[ "length" → 1 ]»
+				: <<angle>>
+				:: the [=CSSNumericValue/type=] is «[ "angle" → 1 ]»
+				: <<time>>
+				:: the [=CSSNumericValue/type=] is «[ "time" → 1 ]»
+				: <<frequency>>
+				:: the [=CSSNumericValue/type=] is «[ "frequency" → 1 ]»
+				: <<resolution>>
+				:: the [=CSSNumericValue/type=] is «[ "resolution" → 1 ]»
+				: <<flex>>
+				:: the [=CSSNumericValue/type=] is «[ "flex" → 1 ]»
+				: <<percentage>>
+				::
+					If, in the context in which the [=math function=]
+					containing this [=calculation=] is placed,
+					<<percentage>>s are resolved relative to another type of value
+					(such as in 'width', where <<percentage>> is resolved against a <<length>>),
+					and that other type is <em>not</em> <<number>>,
+					the [=CSSNumericValue/type=] is determined as the other type.
+
+					Otherwise,
+					the [=CSSNumericValue/type=] is «[ "percent" → 1 ]».
+				: anything else
+				:: The [=calculation’s=] type is failure.
+			</dl>
+
+			In all cases, the associated [=percent hint=] is null.
+	</div>
+
+	[=Math functions=] themselves have [=CSSNumericValue/types=],
+	according to their contained [=calculations=]:
 
 	* The [=CSSNumericValue/type=] of a ''calc()'' expression
-		is the [=CSSNumericValue/type=] of its contained expression.
-		The [=CSSNumericValue/type=] of a ''min()'', ''max()'', or ''clamp()'' expression
+		is the [=CSSNumericValue/type=] of its contained [=calculation=].
+	* The [=CSSNumericValue/type=] of a ''min()'', ''max()'', or ''clamp()'' expression
 		is the result of [=add two types|adding the types=]
-		of its comma-separated expressions.
-		If the result is failure,
-		the entire [=math function=] is invalid.
+		of its comma-separated [=calculations=].
+
+	For each of the above,
+	if the [=CSSNumericValue/type=] is failure,
+	the [=math function=] is invalid.
 
 	A [=math function=] resolves to <<number>>, <<length>>, <<angle>>, <<time>>, <<frequency>>, <<resolution>>, <<flex>>, or <<percentage>>
 	according to which of those productions its [=CSSNumericValue/type=] [=CSSNumericValue/matches=].