diff --git a/lib/lessphp/Cache.php b/lib/lessphp/Cache.php
index e4023ef57c2..8c8be39530e 100644
--- a/lib/lessphp/Cache.php
+++ b/lib/lessphp/Cache.php
@@ -91,7 +91,7 @@ class Less_Cache{
 				self::ListFiles($list_file, $list, $cached_name);
 				$compiled_name = self::CompiledName($list);
 
-				// if $cached_name != $compiled_name, we know we need to recompile
+				// if $cached_name is the same as the $compiled name, don't regenerate
 				if( !$cached_name || $cached_name === $compiled_name ){
 
 					$output_file = self::OutputFile($compiled_name, $parser_options );
@@ -252,7 +252,7 @@ class Less_Cache{
 					continue;
 				}
 
-				$full_path = Less_Cache::$cache_dir.'/'.$file;
+				$full_path = Less_Cache::$cache_dir . $file;
 
 				// make sure the file still exists
 				// css files may have already been deleted
@@ -280,7 +280,7 @@ class Less_Cache{
 				if( $type === 'list' ){
 					self::ListFiles($full_path, $list, $css_file_name);
 					if( $css_file_name ){
-						$css_file = Less_Cache::$cache_dir.'/'.$css_file_name;
+						$css_file = Less_Cache::$cache_dir . $css_file_name;
 						if( file_exists($css_file) ){
 							unlink($css_file);
 						}
@@ -313,4 +313,4 @@ class Less_Cache{
 
 	}
 
-}
\ No newline at end of file
+}
diff --git a/lib/lessphp/Exception/Parser.php b/lib/lessphp/Exception/Parser.php
index 69abd151f0b..d6a419d29bf 100644
--- a/lib/lessphp/Exception/Parser.php
+++ b/lib/lessphp/Exception/Parser.php
@@ -54,7 +54,7 @@ class Less_Exception_Parser extends Exception{
 
 	protected function getInput(){
 
-		if( !$this->input && $this->currentFile && $this->currentFile['filename'] ){
+		if( !$this->input && $this->currentFile && $this->currentFile['filename'] && file_exists($this->currentFile['filename']) ){
 			$this->input = file_get_contents( $this->currentFile['filename'] );
 		}
 	}
diff --git a/lib/lessphp/Functions.php b/lib/lessphp/Functions.php
index e1c68d8119f..419bee32ff5 100644
--- a/lib/lessphp/Functions.php
+++ b/lib/lessphp/Functions.php
@@ -17,11 +17,10 @@ class Less_Functions{
 		$this->currentFileInfo = $currentFileInfo;
 	}
 
-
 	/**
 	 * @param string $op
 	 */
-    public static function operate( $op, $a, $b ){
+	public static function operate( $op, $a, $b ){
 		switch ($op) {
 			case '+': return $a + $b;
 			case '-': return $a - $b;
@@ -47,7 +46,7 @@ class Less_Functions{
 		return $value;
 	}
 
-    public static function number($n){
+	public static function number($n){
 
 		if ($n instanceof Less_Tree_Dimension) {
 			return floatval( $n->unit->is('%') ? $n->value / 100 : $n->value);
@@ -58,7 +57,7 @@ class Less_Functions{
 		}
 	}
 
-    public static function scaled($n, $size = 255 ){
+	public static function scaled($n, $size = 255 ){
 		if( $n instanceof Less_Tree_Dimension && $n->unit->is('%') ){
 			return (float)$n->value * $size / 100;
 		} else {
@@ -66,11 +65,14 @@ class Less_Functions{
 		}
 	}
 
-	public function rgb ($r, $g, $b){
+	public function rgb ($r = null, $g = null, $b = null){
+		if (is_null($r) || is_null($g) || is_null($b)) {
+			throw new Less_Exception_Compiler("rgb expects three parameters");
+		}
 		return $this->rgba($r, $g, $b, 1.0);
 	}
 
-	public function rgba($r, $g, $b, $a){
+	public function rgba($r = null, $g = null, $b = null, $a = null){
 		$rgb = array($r, $g, $b);
 		$rgb = array_map(array('Less_Functions','scaled'),$rgb);
 
@@ -144,59 +146,107 @@ class Less_Functions{
 						 $a);
 	}
 
-	public function hue($color){
+	public function hue($color = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to hue must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$c = $color->toHSL();
 		return new Less_Tree_Dimension(Less_Parser::round($c['h']));
 	}
 
-	public function saturation($color){
+	public function saturation($color = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to saturation must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$c = $color->toHSL();
 		return new Less_Tree_Dimension(Less_Parser::round($c['s'] * 100), '%');
 	}
 
-	public function lightness($color){
+	public function lightness($color = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to lightness must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$c = $color->toHSL();
 		return new Less_Tree_Dimension(Less_Parser::round($c['l'] * 100), '%');
 	}
 
-	public function hsvhue( $color ){
+	public function hsvhue( $color = null ){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to hsvhue must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsv = $color->toHSV();
 		return new Less_Tree_Dimension( Less_Parser::round($hsv['h']) );
 	}
 
 
-	public function hsvsaturation( $color ){
+	public function hsvsaturation( $color = null ){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to hsvsaturation must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsv = $color->toHSV();
 		return new Less_Tree_Dimension( Less_Parser::round($hsv['s'] * 100), '%' );
 	}
 
-	public function hsvvalue( $color ){
+	public function hsvvalue( $color = null ){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to hsvvalue must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsv = $color->toHSV();
 		return new Less_Tree_Dimension( Less_Parser::round($hsv['v'] * 100), '%' );
 	}
 
-	public function red($color) {
+	public function red($color = null) {
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to red must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return new Less_Tree_Dimension( $color->rgb[0] );
 	}
 
-	public function green($color) {
+	public function green($color = null) {
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to green must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return new Less_Tree_Dimension( $color->rgb[1] );
 	}
 
-	public function blue($color) {
+	public function blue($color = null) {
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to blue must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return new Less_Tree_Dimension( $color->rgb[2] );
 	}
 
-	public function alpha($color){
+	public function alpha($color = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to alpha must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$c = $color->toHSL();
 		return new Less_Tree_Dimension($c['a']);
 	}
 
-	public function luma ($color) {
+	public function luma ($color = null) {
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to luma must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return new Less_Tree_Dimension(Less_Parser::round( $color->luma() * $color->alpha * 100), '%');
 	}
 
-	public function luminance( $color ){
+	public function luminance( $color = null ){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to luminance must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$luminance =
 			(0.2126 * $color->rgb[0] / 255)
 		  + (0.7152 * $color->rgb[1] / 255)
@@ -205,12 +255,20 @@ class Less_Functions{
 		return new Less_Tree_Dimension(Less_Parser::round( $luminance * $color->alpha * 100), '%');
 	}
 
-	public function saturate($color, $amount = null){
+	public function saturate($color = null, $amount = null){
 		// filter: saturate(3.2);
 		// should be kept as is, so check for color
-		if( !property_exists($color,'rgb') ){
+		if ($color instanceof Less_Tree_Dimension) {
 			return null;
 		}
+
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to saturate must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to saturate must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 
 		$hsl['s'] += $amount->value / 100;
@@ -222,7 +280,14 @@ class Less_Functions{
 	/**
 	 * @param Less_Tree_Dimension $amount
 	 */
-	public function desaturate($color, $amount){
+	public function desaturate($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to desaturate must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to desaturate must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 
 		$hsl['s'] -= $amount->value / 100;
@@ -233,7 +298,14 @@ class Less_Functions{
 
 
 
-	public function lighten($color, $amount){
+	public function lighten($color = null, $amount=null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to lighten must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to lighten must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 
 		$hsl['l'] += $amount->value / 100;
@@ -242,34 +314,57 @@ class Less_Functions{
 		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
 	}
 
-	public function darken($color, $amount){
-
-		if( $color instanceof Less_Tree_Color ){
-			$hsl = $color->toHSL();
-			$hsl['l'] -= $amount->value / 100;
-			$hsl['l'] = self::clamp($hsl['l']);
-
-			return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
+	public function darken($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to darken must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to darken must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
 		}
 
-		Less_Functions::Expected('color',$color);
+		$hsl = $color->toHSL();
+		$hsl['l'] -= $amount->value / 100;
+		$hsl['l'] = self::clamp($hsl['l']);
+
+		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
 	}
 
-	public function fadein($color, $amount){
+	public function fadein($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to fadein must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to fadein must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 		$hsl['a'] += $amount->value / 100;
 		$hsl['a'] = self::clamp($hsl['a']);
 		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
 	}
 
-	public function fadeout($color, $amount){
+	public function fadeout($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to fadeout must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to fadeout must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 		$hsl['a'] -= $amount->value / 100;
 		$hsl['a'] = self::clamp($hsl['a']);
 		return $this->hsla($hsl['h'], $hsl['s'], $hsl['l'], $hsl['a']);
 	}
 
-	public function fade($color, $amount){
+	public function fade($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to fade must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to fade must be a percentage' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 
 		$hsl['a'] = $amount->value / 100;
@@ -279,7 +374,14 @@ class Less_Functions{
 
 
 
-	public function spin($color, $amount){
+	public function spin($color = null, $amount = null){
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to spin must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$amount instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The second argument to spin must be a number' . ($amount instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		$hsl = $color->toHSL();
 		$hue = fmod($hsl['h'] + $amount->value, 360);
 
@@ -296,10 +398,19 @@ class Less_Functions{
 	/**
 	 * @param Less_Tree_Color $color1
 	 */
-	public function mix($color1, $color2, $weight = null){
+	public function mix($color1 = null, $color2 = null, $weight = null){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to mix must be a color' . ($color1 instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to mix must be a color' . ($color2 instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
 		if (!$weight) {
 			$weight = new Less_Tree_Dimension('50', '%');
 		}
+		if (!$weight instanceof Less_Tree_Dimension) {
+			throw new Less_Exception_Compiler('The third argument to contrast must be a percentage' . ($weight instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
 
 		$p = $weight->value / 100.0;
 		$w = $p * 2 - 1;
@@ -320,14 +431,14 @@ class Less_Functions{
 	}
 
 	public function greyscale($color){
-		return $this->desaturate($color, new Less_Tree_Dimension(100));
+		return $this->desaturate($color, new Less_Tree_Dimension(100,'%'));
 	}
 
 
 	public function contrast( $color, $dark = null, $light = null, $threshold = null){
 		// filter: contrast(3.2);
 		// should be kept as is, so check for color
-		if( !property_exists($color,'rgb') ){
+		if (!$color instanceof Less_Tree_Color) {
 			return null;
 		}
 		if( !$light ){
@@ -336,6 +447,14 @@ class Less_Functions{
 		if( !$dark ){
 			$dark = $this->rgba(0, 0, 0, 1.0);
 		}
+
+		if (!$dark instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to contrast must be a color' . ($dark instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$light instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The third argument to contrast must be a color' . ($light instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		//Figure out which is actually light and dark!
 		if( $dark->luma() > $light->luma() ){
 			$t = $light;
@@ -430,7 +549,7 @@ class Less_Functions{
 		return new Less_Tree_Quoted( $string->quote , $result, $string->escaped);
 	}
 
-    public function unit( $val, $unit = null) {
+	public function unit( $val, $unit = null) {
 		if( !($val instanceof Less_Tree_Dimension) ){
 			throw new Less_Exception_Compiler('The first argument to unit must be a number' . ($val instanceof Less_Tree_Operation ? '. Have you forgotten parenthesis?' : '.') );
 		}
@@ -445,7 +564,7 @@ class Less_Functions{
 			$unit = "";
 		}
 		return new Less_Tree_Dimension($val->value, $unit );
-    }
+	}
 
 	public function convert($val, $unit){
 		return $val->convertTo($unit->value);
@@ -585,7 +704,7 @@ class Less_Functions{
 
 			if( $order[$j]->unit->toString() === "" && $unitClone ){
 				$temp = new Less_Tree_Dimension( $order[$j]->value, $unitClone);
-				$referenceUnified = $temp->unifiy();
+				$referenceUnified = $temp->unify();
 			}else{
 				$referenceUnified = $order[$j]->unify();
 			}
@@ -619,6 +738,10 @@ class Less_Functions{
 	}
 
 	public function argb($color) {
+		if (!$color instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to argb must be a color' . ($dark instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return new Less_Tree_Anonymous($color->toARGB());
 	}
 
@@ -875,21 +998,6 @@ class Less_Functions{
 	}
 
 
-	/**
-	 * @param string $type
-	 */
-	private static function Expected( $type, $arg ){
-
-		$debug = debug_backtrace();
-		array_shift($debug);
-		$last = array_shift($debug);
-		$last = array_intersect_key($last,array('function'=>'','class'=>'','line'=>''));
-
-		$message = 'Object of type '.get_class($arg).' passed to darken function. Expecting `'.$type.'`. '.$arg->toCSS().'. '.print_r($last,true);
-		throw new Less_Exception_Compiler($message);
-
-	}
-
 	/**
 	 * Php version of javascript's `encodeURIComponent` function
 	 *
@@ -924,7 +1032,14 @@ class Less_Functions{
 		return new Less_Tree_Color($r, $ar);
 	}
 
-	public function multiply($color1, $color2 ){
+	public function multiply($color1 = null, $color2 = null ){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to multiply must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to multiply must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendMultiply'),  $color1, $color2 );
 	}
 
@@ -932,7 +1047,14 @@ class Less_Functions{
 		return $cb * $cs;
 	}
 
-	public function screen($color1, $color2 ){
+	public function screen($color1 = null, $color2 = null ){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to screen must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to screen must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendScreen'),  $color1, $color2 );
 	}
 
@@ -940,7 +1062,14 @@ class Less_Functions{
 		return $cb + $cs - $cb * $cs;
 	}
 
-	public function overlay($color1, $color2){
+	public function overlay($color1 = null, $color2 = null){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to overlay must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to overlay must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendOverlay'),  $color1, $color2 );
 	}
 
@@ -951,7 +1080,14 @@ class Less_Functions{
 			: $this->colorBlendScreen($cb - 1, $cs);
 	}
 
-	public function softlight($color1, $color2){
+	public function softlight($color1 = null, $color2 = null){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to softlight must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to softlight must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendSoftlight'),  $color1, $color2 );
 	}
 
@@ -966,7 +1102,14 @@ class Less_Functions{
 		return $cb - (1 - 2 * $cs) * $e * ($d - $cb);
 	}
 
-	public function hardlight($color1, $color2){
+	public function hardlight($color1 = null, $color2 = null){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to hardlight must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to hardlight must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendHardlight'),  $color1, $color2 );
 	}
 
@@ -974,7 +1117,14 @@ class Less_Functions{
 		return $this->colorBlendOverlay($cs, $cb);
 	}
 
-	public function difference($color1, $color2) {
+	public function difference($color1 = null, $color2 = null) {
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to difference must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to difference must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendDifference'),  $color1, $color2 );
 	}
 
@@ -982,7 +1132,14 @@ class Less_Functions{
 		return abs($cb - $cs);
 	}
 
-	public function exclusion( $color1, $color2 ){
+	public function exclusion( $color1 = null, $color2 = null ){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to exclusion must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to exclusion must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendExclusion'),  $color1, $color2 );
 	}
 
@@ -990,7 +1147,14 @@ class Less_Functions{
 		return $cb + $cs - 2 * $cb * $cs;
 	}
 
-	public function average($color1, $color2){
+	public function average($color1 = null, $color2 = null){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to average must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to average must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendAverage'),  $color1, $color2 );
 	}
 
@@ -999,7 +1163,14 @@ class Less_Functions{
 		return ($cb + $cs) / 2;
 	}
 
-	public function negation($color1, $color2 ){
+	public function negation($color1 = null, $color2 = null ){
+		if (!$color1 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The first argument to negation must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+		if (!$color2 instanceof Less_Tree_Color) {
+			throw new Less_Exception_Compiler('The second argument to negation must be a color' . ($color instanceof Less_Tree_Expression ? ' (did you forgot commas?)' : '') );
+		}
+
 		return $this->colorBlend( array($this,'colorBlendNegation'),  $color1, $color2 );
 	}
 
diff --git a/lib/lessphp/LICENSE b/lib/lessphp/LICENSE
new file mode 100644
index 00000000000..82216a5da45
--- /dev/null
+++ b/lib/lessphp/LICENSE
@@ -0,0 +1,178 @@
+
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
+   "Licensor" shall mean the copyright owner or entity authorized by
+   the copyright owner that is granting the License.
+
+   "Legal Entity" shall mean the union of the acting entity and all
+   other entities that control, are controlled by, or are under common
+   control with that entity. For the purposes of this definition,
+   "control" means (i) the power, direct or indirect, to cause the
+   direction or management of such entity, whether by contract or
+   otherwise, or (ii) ownership of fifty percent (50%) or more of the
+   outstanding shares, or (iii) beneficial ownership of such entity.
+
+   "You" (or "Your") shall mean an individual or Legal Entity
+   exercising permissions granted by this License.
+
+   "Source" form shall mean the preferred form for making modifications,
+   including but not limited to software source code, documentation
+   source, and configuration files.
+
+   "Object" form shall mean any form resulting from mechanical
+   transformation or translation of a Source form, including but
+   not limited to compiled object code, generated documentation,
+   and conversions to other media types.
+
+   "Work" shall mean the work of authorship, whether in Source or
+   Object form, made available under the License, as indicated by a
+   copyright notice that is included in or attached to the work
+   (an example is provided in the Appendix below).
+
+   "Derivative Works" shall mean any work, whether in Source or Object
+   form, that is based on (or derived from) the Work and for which the
+   editorial revisions, annotations, elaborations, or other modifications
+   represent, as a whole, an original work of authorship. For the purposes
+   of this License, Derivative Works shall not include works that remain
+   separable from, or merely link (or bind by name) to the interfaces of,
+   the Work and Derivative Works thereof.
+
+   "Contribution" shall mean any work of authorship, including
+   the original version of the Work and any modifications or additions
+   to that Work or Derivative Works thereof, that is intentionally
+   submitted to Licensor for inclusion in the Work by the copyright owner
+   or by an individual or Legal Entity authorized to submit on behalf of
+   the copyright owner. For the purposes of this definition, "submitted"
+   means any form of electronic, verbal, or written communication sent
+   to the Licensor or its representatives, including but not limited to
+   communication on electronic mailing lists, source code control systems,
+   and issue tracking systems that are managed by, or on behalf of, the
+   Licensor for the purpose of discussing and improving the Work, but
+   excluding communication that is conspicuously marked or otherwise
+   designated in writing by the copyright owner as "Not a Contribution."
+
+   "Contributor" shall mean Licensor and any individual or Legal Entity
+   on behalf of whom a Contribution has been received by Licensor and
+   subsequently incorporated within the Work.
+
+2. Grant of Copyright License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   copyright license to reproduce, prepare Derivative Works of,
+   publicly display, publicly perform, sublicense, and distribute the
+   Work and such Derivative Works in Source or Object form.
+
+3. Grant of Patent License. Subject to the terms and conditions of
+   this License, each Contributor hereby grants to You a perpetual,
+   worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+   (except as stated in this section) patent license to make, have made,
+   use, offer to sell, sell, import, and otherwise transfer the Work,
+   where such license applies only to those patent claims licensable
+   by such Contributor that are necessarily infringed by their
+   Contribution(s) alone or by combination of their Contribution(s)
+   with the Work to which such Contribution(s) was submitted. If You
+   institute patent litigation against any entity (including a
+   cross-claim or counterclaim in a lawsuit) alleging that the Work
+   or a Contribution incorporated within the Work constitutes direct
+   or contributory patent infringement, then any patent licenses
+   granted to You under this License for that Work shall terminate
+   as of the date such litigation is filed.
+
+4. Redistribution. You may reproduce and distribute copies of the
+   Work or Derivative Works thereof in any medium, with or without
+   modifications, and in Source or Object form, provided that You
+   meet the following conditions:
+
+   (a) You must give any other recipients of the Work or
+       Derivative Works a copy of this License; and
+
+   (b) You must cause any modified files to carry prominent notices
+       stating that You changed the files; and
+
+   (c) You must retain, in the Source form of any Derivative Works
+       that You distribute, all copyright, patent, trademark, and
+       attribution notices from the Source form of the Work,
+       excluding those notices that do not pertain to any part of
+       the Derivative Works; and
+
+   (d) If the Work includes a "NOTICE" text file as part of its
+       distribution, then any Derivative Works that You distribute must
+       include a readable copy of the attribution notices contained
+       within such NOTICE file, excluding those notices that do not
+       pertain to any part of the Derivative Works, in at least one
+       of the following places: within a NOTICE text file distributed
+       as part of the Derivative Works; within the Source form or
+       documentation, if provided along with the Derivative Works; or,
+       within a display generated by the Derivative Works, if and
+       wherever such third-party notices normally appear. The contents
+       of the NOTICE file are for informational purposes only and
+       do not modify the License. You may add Your own attribution
+       notices within Derivative Works that You distribute, alongside
+       or as an addendum to the NOTICE text from the Work, provided
+       that such additional attribution notices cannot be construed
+       as modifying the License.
+
+   You may add Your own copyright statement to Your modifications and
+   may provide additional or different license terms and conditions
+   for use, reproduction, or distribution of Your modifications, or
+   for any such Derivative Works as a whole, provided Your use,
+   reproduction, and distribution of the Work otherwise complies with
+   the conditions stated in this License.
+
+5. Submission of Contributions. Unless You explicitly state otherwise,
+   any Contribution intentionally submitted for inclusion in the Work
+   by You to the Licensor shall be under the terms and conditions of
+   this License, without any additional terms or conditions.
+   Notwithstanding the above, nothing herein shall supersede or modify
+   the terms of any separate license agreement you may have executed
+   with Licensor regarding such Contributions.
+
+6. Trademarks. This License does not grant permission to use the trade
+   names, trademarks, service marks, or product names of the Licensor,
+   except as required for reasonable and customary use in describing the
+   origin of the Work and reproducing the content of the NOTICE file.
+
+7. Disclaimer of Warranty. Unless required by applicable law or
+   agreed to in writing, Licensor provides the Work (and each
+   Contributor provides its Contributions) on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
+
diff --git a/lib/lessphp/Parser.php b/lib/lessphp/Parser.php
index 6c02bed8635..86d455f1dda 100644
--- a/lib/lessphp/Parser.php
+++ b/lib/lessphp/Parser.php
@@ -47,13 +47,14 @@ class Less_Parser{
 	private $pos;					// current index in `input`
 	private $saveStack = array();	// holds state for backtracking
 	private $furthest;
+	private $mb_internal_encoding = ''; // for remember exists value of mbstring.internal_encoding
 
 	/**
 	 * @var Less_Environment
 	 */
 	private $env;
 
-	private $rules = array();
+	protected $rules = array();
 
 	private static $imports = array();
 
@@ -83,6 +84,14 @@ class Less_Parser{
 			$this->Reset( $env );
 		}
 
+		// mbstring.func_overload > 1 bugfix
+		// The encoding value must be set for each source file,
+		// therefore, to conserve resources and improve the speed of this design is taken here
+		if (ini_get('mbstring.func_overload')) {			
+			$this->mb_internal_encoding = ini_get('mbstring.internal_encoding');
+			@ini_set('mbstring.internal_encoding', 'ascii');
+		}
+
 	}
 
 
@@ -204,17 +213,26 @@ class Less_Parser{
 			}
 
 		} catch (Exception $exc) {
-        	   // Intentional fall-through so we can reset environment
-        	}
+			// Intentional fall-through so we can reset environment
+		}
 
 		//reset php settings
 		@ini_set('precision',$precision);
 		setlocale(LC_NUMERIC, $locale);
 
+		// If you previously defined $this->mb_internal_encoding 
+		// is required to return the encoding as it was before
+		if ($this->mb_internal_encoding != '') {
+			@ini_set("mbstring.internal_encoding", $this->mb_internal_encoding);
+			$this->mb_internal_encoding = '';
+		}
+
 		// Rethrow exception after we handled resetting the environment
 		if (!empty($exc)) {
-            		throw $exc;
-        	}
+			throw $exc;
+		}
+
+
 
 		return $css;
 	}
@@ -285,7 +303,7 @@ class Less_Parser{
 			$filename = 'anonymous-file-'.Less_Parser::$next_id++.'.less';
 		}else{
 			$file_uri = self::WinPath($file_uri);
-			$filename = basename($file_uri);
+			$filename = $file_uri;
 			$uri_root = dirname($file_uri);
 		}
 
@@ -466,17 +484,7 @@ class Less_Parser{
 	 * @param string $file_path
 	 */
 	private function _parse( $file_path = null ){
-		if (ini_get("mbstring.func_overload")) {
-			$mb_internal_encoding = ini_get("mbstring.internal_encoding");
-			@ini_set("mbstring.internal_encoding", "ascii");
-		}
-
 		$this->rules = array_merge($this->rules, $this->GetRules( $file_path ));
-
-		//reset php settings
-		if (isset($mb_internal_encoding)) {
-			@ini_set("mbstring.internal_encoding", $mb_internal_encoding);
-		}
 	}
 
 
diff --git a/lib/lessphp/SourceMap/Generator.php b/lib/lessphp/SourceMap/Generator.php
index ac5f2c92776..cc9e65f369d 100644
--- a/lib/lessphp/SourceMap/Generator.php
+++ b/lib/lessphp/SourceMap/Generator.php
@@ -91,13 +91,9 @@ class Less_SourceMap_Generator extends Less_Configurable {
 		$this->encoder = new Less_SourceMap_Base64VLQ();
 
 		$this->SetOptions($options);
-
-
-		// fix windows paths
-		if( !empty($this->options['sourceMapRootpath']) ){
-			$this->options['sourceMapRootpath'] = str_replace('\\', '/', $this->options['sourceMapRootpath']);
-			$this->options['sourceMapRootpath'] = rtrim($this->options['sourceMapRootpath'],'/').'/';
-		}
+		
+		$this->options['sourceMapRootpath'] = $this->fixWindowsPath($this->options['sourceMapRootpath'], true);
+		$this->options['sourceMapBasepath'] = $this->fixWindowsPath($this->options['sourceMapBasepath'], true);
 	}
 
 	/**
@@ -167,7 +163,8 @@ class Less_SourceMap_Generator extends Less_Configurable {
 	 */
 	protected function normalizeFilename($filename){
 
-		$filename = str_replace('\\', '/', $filename);
+		$filename = $this->fixWindowsPath($filename);
+
 		$rootpath = $this->getOption('sourceMapRootpath');
 		$basePath = $this->getOption('sourceMapBasepath');
 
@@ -350,4 +347,19 @@ class Less_SourceMap_Generator extends Less_Configurable {
 		return $this->source_keys[$filename];
 	}
 
+	/**
+	 * fix windows paths
+	 * @param  string $path
+	 * @return string      
+	 */
+	public function fixWindowsPath($path, $addEndSlash = false){
+		$slash = ($addEndSlash) ? '/' : '';
+		if( !empty($path) ){
+			$path = str_replace('\\', '/', $path);
+			$path = rtrim($path,'/') . $slash;
+		}
+
+		return $path;
+	}
+
 }
\ No newline at end of file
diff --git a/lib/lessphp/Tree/Import.php b/lib/lessphp/Tree/Import.php
index 1752744e9ce..e327b756364 100644
--- a/lib/lessphp/Tree/Import.php
+++ b/lib/lessphp/Tree/Import.php
@@ -232,6 +232,14 @@ class Less_Tree_Import extends Less_Tree{
 						return array( $full_path, $uri );
 					}
 				}elseif( !empty($rootpath) ){
+
+
+					if( $rooturi ){
+						if( strpos($evald_path,$rooturi) === 0 ){
+							$evald_path = substr( $evald_path, strlen($rooturi) );
+						}
+					}
+
 					$path = rtrim($rootpath,'/\\').'/'.ltrim($evald_path,'/\\');
 
 					if( file_exists($path) ){
diff --git a/lib/lessphp/Version.php b/lib/lessphp/Version.php
index 1e95433382e..704ec6e07b3 100644
--- a/lib/lessphp/Version.php
+++ b/lib/lessphp/Version.php
@@ -8,8 +8,8 @@
  */
 class Less_Version{
 
-	const version = '1.7.0.3';			// The current build number of less.php
+	const version = '1.7.0.9';			// The current build number of less.php
 	const less_version = '1.7';			// The less.js version that this build should be compatible with
     const cache_version = '170';		// The parser cache version
 
-}
\ No newline at end of file
+}
diff --git a/lib/lessphp/moodle_readme.txt b/lib/lessphp/moodle_readme.txt
index fac01409a44..3e748dc63ab 100644
--- a/lib/lessphp/moodle_readme.txt
+++ b/lib/lessphp/moodle_readme.txt
@@ -8,5 +8,7 @@ All the files from the folder lib/Less are copied in
 this directory. Only exception made for the directory
 '.easymin' which is not included.
 
+Also copy the license file from the project root.
+
 Licensed under the Apache license 2.0.
 
diff --git a/lib/thirdpartylibs.xml b/lib/thirdpartylibs.xml
index d560b630485..7fe18de6b42 100644
--- a/lib/thirdpartylibs.xml
+++ b/lib/thirdpartylibs.xml
@@ -32,7 +32,7 @@
     <location>lessphp</location>
     <name>less.php</name>
     <license>Apache</license>
-    <version>1.7.0.3</version>
+    <version>1.7.0.9</version>
     <licenseversion>2.0</licenseversion>
   </library>
   <library>
diff --git a/lib/upgrade.txt b/lib/upgrade.txt
index 5d25e3f6da9..2fd5c600643 100644
--- a/lib/upgrade.txt
+++ b/lib/upgrade.txt
@@ -3,6 +3,7 @@ information provided here is intended especially for developers.
 
 === 3.0 ===
 
+* Less.php upgraded to 1.7.0.9
 * External functions x_is_allowed_from_ajax() methods have been deprecated. Define 'ajax' => true in db/services.php instead.
 * External functions can be called without a session if they define 'loginrequired' => true in db/services.php.
 * All plugins are required to declare their frankenstyle component name via