diff --git a/lib/Less/Functions.php b/lib/Less/Functions.php
index 1f7a2231..a32ae17d 100644
--- a/lib/Less/Functions.php
+++ b/lib/Less/Functions.php
@@ -170,7 +170,7 @@ public function hue( $color = null ) {
 		}
 
 		$c = $color->toHSL();
-		return new Less_Tree_Dimension( Less_Parser::round( $c['h'] ) );
+		return new Less_Tree_Dimension( $c['h'] );
 	}
 
 	public function saturation( $color = null ) {
@@ -179,7 +179,7 @@ public function saturation( $color = null ) {
 		}
 
 		$c = $color->toHSL();
-		return new Less_Tree_Dimension( Less_Parser::round( $c['s'] * 100 ), '%' );
+		return new Less_Tree_Dimension( $c['s'] * 100, '%' );
 	}
 
 	public function lightness( $color = null ) {
@@ -188,7 +188,7 @@ public function lightness( $color = null ) {
 		}
 
 		$c = $color->toHSL();
-		return new Less_Tree_Dimension( Less_Parser::round( $c['l'] * 100 ), '%' );
+		return new Less_Tree_Dimension( $c['l'] * 100, '%' );
 	}
 
 	public function hsvhue( $color = null ) {
@@ -197,7 +197,7 @@ public function hsvhue( $color = null ) {
 		}
 
 		$hsv = $color->toHSV();
-		return new Less_Tree_Dimension( Less_Parser::round( $hsv['h'] ) );
+		return new Less_Tree_Dimension( $hsv['h'] );
 	}
 
 	public function hsvsaturation( $color = null ) {
@@ -206,7 +206,7 @@ public function hsvsaturation( $color = null ) {
 		}
 
 		$hsv = $color->toHSV();
-		return new Less_Tree_Dimension( Less_Parser::round( $hsv['s'] * 100 ), '%' );
+		return new Less_Tree_Dimension( $hsv['s'] * 100, '%' );
 	}
 
 	public function hsvvalue( $color = null ) {
@@ -215,7 +215,7 @@ public function hsvvalue( $color = null ) {
 		}
 
 		$hsv = $color->toHSV();
-		return new Less_Tree_Dimension( Less_Parser::round( $hsv['v'] * 100 ), '%' );
+		return new Less_Tree_Dimension( $hsv['v'] * 100, '%' );
 	}
 
 	public function red( $color = null ) {
@@ -256,7 +256,7 @@ public function luma( $color = null ) {
 			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 ), '%' );
+		return new Less_Tree_Dimension( $color->luma() * $color->alpha * 100, '%' );
 	}
 
 	public function luminance( $color = null ) {
@@ -269,10 +269,10 @@ public function luminance( $color = null ) {
 		  + ( 0.7152 * $color->rgb[1] / 255 )
 		  + ( 0.0722 * $color->rgb[2] / 255 );
 
-		return new Less_Tree_Dimension( Less_Parser::round( $luminance * $color->alpha * 100 ), '%' );
+		return new Less_Tree_Dimension( $luminance * $color->alpha * 100, '%' );
 	}
 
-	public function saturate( $color = null, $amount = null ) {
+	public function saturate( $color = null, $amount = null, $method = null ) {
 		// filter: saturate(3.2);
 		// should be kept as is, so check for color
 		if ( $color instanceof Less_Tree_Dimension ) {
@@ -288,8 +288,11 @@ public function saturate( $color = null, $amount = null ) {
 
 		$hsl = $color->toHSL();
 
-		$hsl['s'] += $amount->value / 100;
-		$hsl['s'] = self::clamp( $hsl['s'] );
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['s'] += $hsl['s'] * $amount->value / 100;
+		} else {
+			$hsl['s'] += $amount->value / 100;
+		}		$hsl['s'] = self::clamp( $hsl['s'] );
 
 		return $this->hsla( $hsl['h'], $hsl['s'], $hsl['l'], $hsl['a'] );
 	}
@@ -298,7 +301,7 @@ public function saturate( $color = null, $amount = null ) {
 	 * @param Less_Tree_Color|null $color
 	 * @param Less_Tree_Dimension|null $amount
 	 */
-	public function desaturate( $color = null, $amount = null ) {
+	public function desaturate( $color = null, $amount = null, $method = null ) {
 		if ( !$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?)' : '' ) );
 		}
@@ -307,13 +310,19 @@ public function desaturate( $color = null, $amount = null ) {
 		}
 
 		$hsl = $color->toHSL();
-		$hsl['s'] -= $amount->value / 100;
+
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['s'] -= $hsl['s'] * $amount->value / 100;
+		} else {
+			$hsl['s'] -= $amount->value / 100;
+		}
+
 		$hsl['s'] = self::clamp( $hsl['s'] );
 
 		return $this->hsla( $hsl['h'], $hsl['s'], $hsl['l'], $hsl['a'] );
 	}
 
-	public function lighten( $color = null, $amount = null ) {
+	public function lighten( $color = null, $amount = null, $method = null ) {
 		if ( !$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?)' : '' ) );
 		}
@@ -323,13 +332,18 @@ public function lighten( $color = null, $amount = null ) {
 
 		$hsl = $color->toHSL();
 
-		$hsl['l'] += $amount->value / 100;
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['l'] += $hsl['l'] * $amount->value / 100;
+		} else {
+			$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 ) {
+	public function darken( $color = null, $amount = null, $method = null ) {
 		if ( !$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?)' : '' ) );
 		}
@@ -338,13 +352,17 @@ public function darken( $color = null, $amount = null ) {
 		}
 
 		$hsl = $color->toHSL();
-		$hsl['l'] -= $amount->value / 100;
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['l'] -= $hsl['l'] * $amount->value / 100;
+		} else {
+			$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 = null, $amount = null ) {
+	public function fadein( $color = null, $amount = null, $method = null ) {
 		if ( !$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?)' : '' ) );
 		}
@@ -353,12 +371,18 @@ public function fadein( $color = null, $amount = null ) {
 		}
 
 		$hsl = $color->toHSL();
-		$hsl['a'] += $amount->value / 100;
+
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['a'] += $hsl['a'] * $amount->value / 100;
+		} else {
+			$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 = null, $amount = null ) {
+	public function fadeout( $color = null, $amount = null, $method = null ) {
 		if ( !$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?)' : '' ) );
 		}
@@ -367,7 +391,13 @@ public function fadeout( $color = null, $amount = null ) {
 		}
 
 		$hsl = $color->toHSL();
-		$hsl['a'] -= $amount->value / 100;
+
+		if ( isset( $method ) && $method->value === "relative" ) {
+			$hsl['a'] -= $hsl['a'] * $amount->value / 100;
+		} else {
+			$hsl['a'] -= $amount->value / 100;
+		}
+
 		$hsl['a'] = self::clamp( $hsl['a'] );
 		return $this->hsla( $hsl['h'], $hsl['s'], $hsl['l'], $hsl['a'] );
 	}
@@ -514,10 +544,16 @@ public function replace( $string, $pattern, $replacement, $flags = null ) {
 		if ( $flags && $flags->value ) {
 			$expr .= self::replace_flags( $flags->value );
 		}
+		$replacement = ( $replacement instanceof Less_Tree_Quoted ) ?
+			$replacement->value : $replacement->toCSS();
 
-		$result = preg_replace( $expr, $replacement->value, $result );
+		$result = preg_replace( $expr, $replacement, $result, 1 );
 
-		if ( property_exists( $string, 'quote' ) ) {
+		if ( $flags && $flags->value && preg_match( '/g/', $flags->value ) ) {
+			$result = preg_replace( $expr, $replacement, $result );
+		}
+
+		if ( $string instanceof Less_Tree_Quoted ) {
 			return new Less_Tree_Quoted( $string->quote, $result, $string->escaped );
 		}
 		return new Less_Tree_Quoted( '', $result );
@@ -533,14 +569,19 @@ public function _percent( $string, ...$args ) {
 		foreach ( $args as $arg ) {
 			if ( preg_match( '/%[sda]/i', $result, $token ) ) {
 				$token = $token[0];
-				$value = stristr( $token, 's' ) ? $arg->value : $arg->toCSS();
+				$value = ( ( $arg instanceof Less_Tree_Quoted ) &&
+					stristr( $token, 's' ) ? $arg->value : $arg->toCSS() );
+
 				$value = preg_match( '/[A-Z]$/', $token ) ? urlencode( $value ) : $value;
 				$result = preg_replace( '/%[sda]/i', $value, $result, 1 );
 			}
 		}
 		$result = str_replace( '%%', '%', $result );
 
-		return new Less_Tree_Quoted( $string->quote, $result, $string->escaped );
+		 if ( $string instanceof Less_Tree_Quoted ) {
+			 return new Less_Tree_Quoted( $string->quote, $result, $string->escaped );
+		 }
+		return new Less_Tree_Quoted( '', $result );
 	}
 
 	public function unit( $val, $unit = null ) {
@@ -781,6 +822,10 @@ public function color( $c ) {
 		throw new Less_Exception_Compiler( "argument must be a color keyword or 3/6 digit hex e.g. #FFF" );
 	}
 
+	public function isruleset( $n ) {
+		return new Less_Tree_Keyword( $n instanceof Less_Tree_DetachedRuleset ? 'true' : 'false' );
+	}
+
 	public function iscolor( $n ) {
 		return new Less_Tree_Keyword( $n instanceof Less_Tree_Color ? 'true' : 'false' );
 	}
diff --git a/lib/Less/Parser.php b/lib/Less/Parser.php
index 621c6091..f6d98098 100644
--- a/lib/Less/Parser.php
+++ b/lib/Less/Parser.php
@@ -1241,7 +1241,7 @@ private function parseEntitiesDimension() {
 			return;
 		}
 
-		$value = $this->MatchReg( '/\\G([+-]?\d*\.?\d+)(%|[a-z]+)?/' );
+		$value = $this->MatchReg( '/\\G([+-]?\d*\.?\d+)(%|[a-z]+)?/i' );
 		if ( $value ) {
 			if ( isset( $value[2] ) ) {
 				return new Less_Tree_Dimension( $value[1], $value[2] );
diff --git a/lib/Less/Tree/Call.php b/lib/Less/Tree/Call.php
index ab3d3a7c..0581d5da 100644
--- a/lib/Less/Tree/Call.php
+++ b/lib/Less/Tree/Call.php
@@ -46,6 +46,17 @@ public function compile( $env = null ) {
 			$args[] = $a->compile( $env );
 		}
 
+		foreach ( $args as $key => $arg ) {
+			if ( $arg instanceof Less_Tree_Expression ) {
+				$arg->throwAwayComments();
+
+				if ( count( $arg->value ) === 1 ) {
+					$subNode = $arg->value[0];
+					array_splice( $args, $key, 1, [ $subNode ] );
+				}
+			}
+		}
+
 		Less_Environment::$mathOn = $currentMathContext;
 
 		$nameLC = strtolower( $this->name );
diff --git a/lib/Less/Tree/Quoted.php b/lib/Less/Tree/Quoted.php
index e9d199e2..2b67e868 100644
--- a/lib/Less/Tree/Quoted.php
+++ b/lib/Less/Tree/Quoted.php
@@ -13,7 +13,7 @@ class Less_Tree_Quoted extends Less_Tree implements Less_Tree_HasValueProperty {
 	/**
 	 * @param string $str
 	 */
-	public function __construct( $str, $content = '', $escaped = false, $index = false, $currentFileInfo = null ) {
+	public function __construct( $str, $content = '', $escaped = true, $index = false, $currentFileInfo = null ) {
 		$this->escaped = $escaped;
 		$this->value = $content;
 		if ( $str ) {
diff --git a/lib/Less/Tree/Unit.php b/lib/Less/Tree/Unit.php
index c4e8fcf1..983e4546 100644
--- a/lib/Less/Tree/Unit.php
+++ b/lib/Less/Tree/Unit.php
@@ -50,7 +50,7 @@ public function compare( $other ) {
 	}
 
 	public function is( $unitString ) {
-		return $this->toString() === $unitString;
+		return strtoupper( $this->toString() ) === strtoupper( $unitString );
 	}
 
 	public function isLength() {
diff --git a/test/Fixtures/bug-reports/css/210.css b/test/Fixtures/bug-reports/css/210.css
index 4409eed7..cc0b757a 100644
--- a/test/Fixtures/bug-reports/css/210.css
+++ b/test/Fixtures/bug-reports/css/210.css
@@ -4,14 +4,14 @@ body .color-channels {
   --saturation: 50%;
   --lightness: 40%;
   --hsvhue: 210;
-  --hsvsaturation: 67%;
+  --hsvsaturation: 66.66666667%;
   --hsvvalue: 60%;
   --red: 51;
   --green: 102;
   --blue: 153;
   --alpha: 0.9;
-  --luma: 11%;
-  --luminance: 33%;
+  --luma: 11.25581169%;
+  --luminance: 33.4728%;
 }
 body .color-definitions .rgb {
   color: #336699;
@@ -29,10 +29,10 @@ body .color-definitions .hsla {
   color: rgba(51, 102, 153, 0.9);
 }
 body .color-definitions .hsv {
-  color: #326699;
+  color: #336699;
 }
 body .color-definitions .hsva {
-  color: rgba(50, 102, 153, 0.9);
+  color: rgba(51, 102, 153, 0.9);
 }
 body .css-filters .saturate {
   color: saturate(200%);
diff --git a/test/Fixtures/lessjs-2.5.3/expected/functions.css b/test/Fixtures/lessjs-2.5.3/expected/functions.css
index ab5df5bb..0b9b344c 100644
--- a/test/Fixtures/lessjs-2.5.3/expected/functions.css
+++ b/test/Fixtures/lessjs-2.5.3/expected/functions.css
@@ -27,7 +27,7 @@
   luma-green: 71.52%;
   luma-blue: 7.22%;
   luma-yellow: 92.78%;
-  luma-cyan: 78.74%;
+  luma-cyan: 78.73999999999999%;
   luma-differs-from-luminance: 23.89833349%;
   luminance-white: 100%;
   luminance-black: 0%;
@@ -96,12 +96,12 @@
   pi: 3.14159265;
   mod: 2m;
   abs: 4%;
-  tan: 0.90040404;
-  sin: 0.17364818;
+  tan: 0.90040415;
+  sin: 0.17364819;
   cos: 0.84385396;
   atan: 0.1rad;
   atan: 34deg;
-  atan: 45deg;
+  atan: 44.9999964deg;
   pow: 64px;
   pow: 64;
   pow: 27;
diff --git a/test/phpunit/FixturesTest.php b/test/phpunit/FixturesTest.php
index 6e727b69..704bbbee 100644
--- a/test/phpunit/FixturesTest.php
+++ b/test/phpunit/FixturesTest.php
@@ -25,9 +25,6 @@ class phpunit_FixturesTest extends phpunit_bootstrap {
 			// If T352866 is fixed, this is should also be resolved
 			'variables' => true,
 
-			// Temporary disabled; Bug logged here T353289
-			'functions' => true,
-
 			// Temporary disabled; Bug logged here T352859
 			'selectors' => true,
 
@@ -122,6 +119,9 @@ public function testFixture( $cssFile, $lessFile ) {
 		// Check with standard parser
 		$parser = new Less_Parser();
 		try {
+			$parser->registerFunction( '_color', [ __CLASS__, 'FnColor' ] );
+			$parser->registerFunction( 'add', [ __CLASS__, 'FnAdd' ] );
+			$parser->registerFunction( 'increment', [ __CLASS__, 'FnIncrement' ] );
 			$parser->parseFile( $lessFile );
 			$css = $parser->getCss();
 		} catch ( Less_Exception_Parser $e ) {
@@ -131,7 +131,10 @@ public function testFixture( $cssFile, $lessFile ) {
 		$this->assertSame( $expectedCSS, $css, "Standard compiler" );
 
 		// Check with cache
-		$options = [ 'cache_dir' => $this->cache_dir ];
+		$options = [ 'cache_dir' => $this->cache_dir,
+					 'functions' => [ '_color' => [ __CLASS__, 'FnColor' ],
+									  'add' => [ __CLASS__, 'FnAdd' ],
+									  'increment' => [ __CLASS__, 'FnIncrement' ] ] ];
 		$files = [ $lessFile => '' ];
 		try {
 			$cacheFile = Less_Cache::Regen( $files, $options );
@@ -152,4 +155,19 @@ public function testFixture( $cssFile, $lessFile ) {
 		$css = trim( $css );
 		$this->assertEquals( $expectedCSS, $css, "Using cache" );
 	}
+
+	public static function FnColor( $str ) {
+		if ( $str->value === "evil red" ) {
+			return new Less_Tree_Color( "600" );
+		}
+	}
+
+	public static function FnAdd( $a, $b ) {
+		return new Less_Tree_Dimension( $a->value + $b->value );
+	}
+
+	public static function FnIncrement( $a ) {
+		return new Less_Tree_Dimension( $a->value + 1 );
+	}
+
 }