CSS: Justify use of rtrim on CSS property values

gibson042 · mgol · commit a1373e2e4f73 · 2022-01-03T14:07:49.000+01:00
CSS does not acknowledge carriage return or form feed characters as whitespace but it does replace them with whitespace, making it acceptable to use `rtrim`. Closes gh-4956 (cherry picked from commit 655c0ed)
diff --git a/src/css/curCSS.js b/src/css/curCSS.js
@@ -32,6 +32,12 @@ function curCSS( elem, name, computed ) {
 
 		// trim whitespace for custom property (issue gh-4926)
 		if ( isCustomProp ) {
+
+			// rtrim treats U+000D CARRIAGE RETURN and U+000C FORM FEED
+			// as whitespace while CSS does not, but this is not a problem
+			// because CSS preprocessing replaces them with U+000A LINE FEED
+			// (which *is* CSS whitespace)
+			// https://www.w3.org/TR/css-syntax-3/#input-preprocessing
 			ret = ret.replace( rtrimCSS, "$1" );
 		}
 
