Fixes #10021. Allow negative relative values for `.css()` (e.g., `"+=-20px"`)...

Fixes #10021. Allow negative relative values for `.css()` (e.g., `"+=-20px"`) since `.animate()` already allows it. Useful for when the relative value is a variable.

src/css.js

@@ -6,8 +6,7 @@ var ralpha = /alpha\([^)]*\)/i,
 	rupper = /([A-Z]|^ms)/g,
 	rnumpx = /^-?\d+(?:px)?$/i,
 	rnum = /^-?\d/,
-	rrelNum = /^[+\-]=/,
-	rrelNumFilter = /[^+\-\.\de]+/g,
+	rrelNum = /^([+\-])=([+\-\.\de]+)/,
 
 	cssShow = { position: "absolute", visibility: "hidden", display: "block" },
 	cssWidth = [ "Left", "Right" ],
@@ -84,18 +83,18 @@ jQuery.extend({
 		if ( value !== undefined ) {
 			type = typeof value;
 
-			// Make sure that NaN and null values aren't set. See: #7116
-			if ( type === "number" && isNaN( value ) || value == null ) {
-				return;
-			}
-
 			// convert relative number strings (+= or -=) to relative numbers. #7345
-			if ( type === "string" && rrelNum.test( value ) ) {
-				value = +value.replace( rrelNumFilter, "" ) + parseFloat( jQuery.css( elem, name ) );
+			if ( type === "string" && (ret = rrelNum.exec( value )) ) {
+				value = (ret[1] === "+"? +ret[2] : -ret[2]) + parseFloat( jQuery.css( elem, name ) );
 				// Fixes bug #9237
 				type = "number";
 			}
 
+			// Make sure that NaN and null values aren't set. See: #7116
+			if ( type === "number" && isNaN( value ) || value == null ) {
+				return;
+			}
+
 			// If a number was passed in, add 'px' to the (except for certain CSS properties)
 			if ( type === "number" && !jQuery.cssNumber[ origName ] ) {
 				value += "px";

test/unit/css.js

@@ -109,7 +109,7 @@ test("css(String|Hash)", function() {
 });
 
 test("css() explicit and relative values", function() {
-	expect(27);
+	expect(29);
 	var $elem = jQuery("#nothiddendiv");
 
 	$elem.css({ width: 1, height: 1, paddingLeft: "1px", opacity: 1 });
@@ -141,6 +141,12 @@ test("css() explicit and relative values", function() {
 	$elem.css( "width", "-=9px" );
 	equals( $elem.width(), 1, "'-=9px' on width (params)" );
 
+	$elem.css( "width", "-=-9px" );
+	equals( $elem.width(), 10, "'-=-9px' on width (params)" );
+
+	$elem.css( "width", "+=-9px" );
+	equals( $elem.width(), 1, "'+=-9px' on width (params)" );
+
 	$elem.css({ paddingLeft: "+=4" });
 	equals( $elem.css("paddingLeft"), "5px", "'+=4' on paddingLeft (hash)" );