[css-values-4] Allow B in round() to be omitted, default to 1. w3c#9668

Author: tabatkins

css-values-4/Overview.bs

@@ -3259,7 +3259,7 @@ Stepped Value Functions: ''round()'', ''mod()'', and ''rem()''</h3>
 	according to another "step value",
 	in different ways.
 
-	The <dfn lt="round()">round(<<rounding-strategy>>?, A, B)</dfn> function
+	The <dfn lt="round()">round(<<rounding-strategy>>?, A, B?)</dfn> function
 	contains an optional rounding strategy,
 	and two [=calculations=] A and B,
 	and returns the value of A,
@@ -3302,6 +3302,11 @@ Stepped Value Functions: ''round()'', ''mod()'', and ''rem()''</h3>
 	If <<rounding-strategy>> is omitted,
 	it defaults to ''nearest''.
 	(Aka [=rounding to the nearest integer=].)
+	If the [=CSSNumericValue/type=] of A
+	matches <<number>>,
+	then B may be omitted,
+	and defaults to ''1'';
+	omitting B is otherwise invalid.
 
 	Issue(5689): CSSOM needs to specify how it rounds,
 	and it's probably good for CSS functions to round the same way by default.
@@ -5531,6 +5536,8 @@ Recent Changes</h3>
 		and added one on 'scrollbar-gutter'
 		to make it possible for 100 of these units to actually match the [=initial containing block=].
 		(<a href="https://github.com/w3c/csswg-drafts/issues/6026">Issue 6026</a>)
+	* Allow B to be omitted in ''round()'' if the A's type is <<number>>.
+		(<a href="https://github.com/w3c/csswg-drafts/issues/9668">Issue 9668</a>)
 
 	Substantial changes since <a href="https://www.w3.org/TR/2023/WD-css-values-4-20231027/">27 October 2023 WD</a>: