Selector: Allow whitespace after hex escapes in CSS identifiers

Ref jquery/jquery#4424
Closes gh-450

dist/sizzle.js

@@ -6,7 +6,7 @@
  * Released under the MIT license
  * https://js.foundation/
  *
- * Date: 2019-05-29
+ * Date: 2019-07-02
  */
 ( function( window ) {
 var i,
@@ -76,8 +76,9 @@ var i,
 	// http://www.w3.org/TR/css3-selectors/#whitespace
 	whitespace = "[\\x20\\t\\r\\n\\f]",
 
-	// http://www.w3.org/TR/CSS21/syndata.html#value-def-identifier
-	identifier = "(?:\\\\.|[\\w-]|[^\0-\\xa0])+",
+	// https://www.w3.org/TR/css-syntax-3/#ident-token-diagram
+	identifier = "(?:\\\\[\\da-fA-F]{1,6}" + whitespace +
+		"?|\\\\[^\\r\\n\\f]|[\\w-]|[^\0-\\x7f])+",
 
 	// Attribute selectors: http://www.w3.org/TR/selectors/#attribute-selectors
 	attributes = "\\[" + whitespace + "*(" + identifier + ")(?:" + whitespace +
@@ -147,22 +148,21 @@ var i,
 
 	// CSS escapes
 	// http://www.w3.org/TR/CSS21/syndata.html#escaped-characters
-	runescape = new RegExp( "\\\\([\\da-f]{1,6}" + whitespace + "?|(" + whitespace +
-		")|.)", "ig" ),
-	funescape = function( _, escaped, escapedWhitespace ) {
-		var high = "0x" + escaped - 0x10000;
-
-		// NaN means non-codepoint
-		// Support: Firefox<24
-		// Workaround erroneous numeric interpretation of +"0x"
-		return high !== high || escapedWhitespace ?
-			escaped :
-			high < 0 ?
+	runescape = new RegExp( "\\\\[\\da-fA-F]{1,6}" + whitespace + "?|\\\\([^\\r\\n\\f])", "g" ),
+	funescape = function( escape, nonHex ) {
+		var high = "0x" + escape.slice( 1 ) - 0x10000;
 
-				// BMP codepoint
-				String.fromCharCode( high + 0x10000 ) :
+		return nonHex ?
+
+			// Strip the backslash prefix from a non-hex escape sequence
+			nonHex :
 
-				// Supplemental Plane codepoint (surrogate pair)
+			// Replace a hexadecimal escape sequence with the encoded Unicode code point
+			// Support: IE <=11+
+			// For values outside the Basic Multilingual Plane (BMP), manually construct a
+			// surrogate pair
+			high < 0 ?
+				String.fromCharCode( high + 0x10000 ) :
 				String.fromCharCode( high >> 10 | 0xD800, high & 0x3FF | 0xDC00 );
 	},