[css-values-4] Better define how math functions combine their argument types. #10017

Author: tabatkins

css-values-4/Overview.bs

@@ -3147,9 +3147,9 @@ Comparison Functions: ''min()'', ''max()'', and ''clamp()''</h3>
 
 	For all three functions,
 	the argument [=calculations=] can resolve to any <<number>>, <<dimension>>, or <<percentage>>,
-	but must have the <em>same</em> [=determine the type of a calculation|type=],
+	but must have a [=consistent type=]
 	or else the function is invalid;
-	the result will have the same [=CSSNumericValue/type=] as the arguments.
+	the result's type will be the [=consistent type=].
 
 	<div class="example">
 
@@ -3240,9 +3240,9 @@ Stepped Value Functions: ''round()'', ''mod()'', and ''rem()''</h3>
 	rounded according to the rounding strategy,
 	to the nearest integer multiple of B either above or below A.
 	The argument [=calculations=] can resolve to any <<number>>, <<dimension>>, or <<percentage>>,
-	but must have the <em>same</em> [=determine the type of a calculation|type=],
+	but must have a [=consistent type=]
 	or else the function is invalid;
-	the result will have the same [=CSSNumericValue/type=] as the arguments.
+	the result's type will be the [=consistent type=].
 
 	If A is exactly equal to an integer multiple of B,
 	''round()'' resolves to A exactly
@@ -3503,7 +3503,7 @@ Trigonometric Functions: ''sin()'', ''cos()'', ''tan()'', ''asin()'', ''acos()''
 	The <dfn lt="atan2()">atan2(A, B)</dfn> function
 	contains two comma-separated [=calculations=], A and B.
 	A and B can resolve to any <<number>>, <<dimension>>, or <<percentage>>,
-	but must have the <em>same</em> [=determine the type of a calculation|type=],
+	but must have a [=consistent type=]
 	or else the function is invalid.
 	The function returns the <<angle>>
 	between the positive X-axis and the point (B,A).
@@ -3706,9 +3706,9 @@ Exponential  Functions: ''pow()'', ''sqrt()'', ''hypot()'', ''log()'', ''exp()''
 	(That is,
 	the square root of the sum of the squares of its arguments.)
 	The argument [=calculations=] can resolve to any <<number>>, <<dimension>>, or <<percentage>>,
-	but must have the <em>same</em> [=determine the type of a calculation|type=],
+	but must have a [=consistent type=]
 	or else the function is invalid;
-	the result will have the same [=CSSNumericValue/type=] as the arguments.
+	the result's type will be the [=consistent type=].
 
 	<details class=note>
 		<summary>Why does ''hypot()'' allow dimensions (values with units), but ''pow()'' and ''sqrt()'' only work on numbers?</summary>
@@ -4321,6 +4321,12 @@ Type Checking</h3>
 			</dl>
 	</div>
 
+	<div algorithm>
+		Two or more calculations have a <dfn export local-lt="consistent">consistent type</dfn>
+		if [=add two types/adding the types=] doesn't result in failure.
+		The [=consistent type=] is the result of the type addition.
+	</div>
+
 	[=Math functions=] themselves have [=CSSNumericValue/types=],
 	according to their contained [=calculations=]: