diff --git a/.travis.yml b/.travis.yml
index c6ad6600..2d3418f6 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,6 +4,8 @@ php:
     - "5.3"
     - "5.5"
     - "5.6"
+    - "7.0"
+    - "nightly"
     - hhvm
 script: phpunit .
 
diff --git a/README.md b/README.md
index 2297e9f2..68833f65 100644
--- a/README.md
+++ b/README.md
@@ -88,7 +88,7 @@ If you want to manipulate a `RuleSet`, use the methods `addRule(Rule $oRule)`, `
 
 * `Size` – consists of a numeric `size` value and a unit.
 * `Color` – colors can be input in the form #rrggbb, #rgb or schema(val1, val2, …) but are always stored as an array of ('s' => val1, 'c' => val2, 'h' => val3, …) and output in the second form.
-* `String` – this is just a wrapper for quoted strings to distinguish them from keywords; always output with double quotes.
+* `CSSString` – this is just a wrapper for quoted strings to distinguish them from keywords; always output with double quotes.
 * `URL` – URLs in CSS; always output in URL("") notation.
 
 There is another abstract subclass of `Value`, `ValueList`. A `ValueList` represents a lists of `Value`s, separated by some separation character (mostly `,`, whitespace, or `/`). There are two types of `ValueList`s:
@@ -193,8 +193,8 @@ To see what you can do with output formatting, look at the tests in `tests/Sabbe
 	    [0]=>
 	    object(Sabberworm\CSS\Property\Charset)#6 (1) {
 	      ["sCharset":"Sabberworm\CSS\Property\Charset":private]=>
-	      object(Sabberworm\CSS\Value\String)#5 (1) {
-	        ["sString":"Sabberworm\CSS\Value\String":private]=>
+	      object(Sabberworm\CSS\Value\CSSString)#5 (1) {
+	        ["sString":"Sabberworm\CSS\Value\CSSString":private]=>
 	        string(5) "utf-8"
 	      }
 	    }
@@ -211,8 +211,8 @@ To see what you can do with output formatting, look at the tests in `tests/Sabbe
 	            ["sRule":"Sabberworm\CSS\Rule\Rule":private]=>
 	            string(11) "font-family"
 	            ["mValue":"Sabberworm\CSS\Rule\Rule":private]=>
-	            object(Sabberworm\CSS\Value\String)#9 (1) {
-	              ["sString":"Sabberworm\CSS\Value\String":private]=>
+	            object(Sabberworm\CSS\Value\CSSString)#9 (1) {
+	              ["sString":"Sabberworm\CSS\Value\CSSString":private]=>
 	              string(10) "CrassRoots"
 	            }
 	            ["bIsImportant":"Sabberworm\CSS\Rule\Rule":private]=>
@@ -228,8 +228,8 @@ To see what you can do with output formatting, look at the tests in `tests/Sabbe
 	            ["mValue":"Sabberworm\CSS\Rule\Rule":private]=>
 	            object(Sabberworm\CSS\Value\URL)#11 (1) {
 	              ["oURL":"Sabberworm\CSS\Value\URL":private]=>
-	              object(Sabberworm\CSS\Value\String)#12 (1) {
-	                ["sString":"Sabberworm\CSS\Value\String":private]=>
+	              object(Sabberworm\CSS\Value\CSSString)#12 (1) {
+	                ["sString":"Sabberworm\CSS\Value\CSSString":private]=>
 	                string(15) "../media/cr.ttf"
 	              }
 	            }
@@ -469,8 +469,8 @@ To see what you can do with output formatting, look at the tests in `tests/Sabbe
 	                [1]=>
 	                string(9) "Helvetica"
 	                [2]=>
-	                object(Sabberworm\CSS\Value\String)#14 (1) {
-	                  ["sString":"Sabberworm\CSS\Value\String":private]=>
+	                object(Sabberworm\CSS\Value\CSSString)#14 (1) {
+	                  ["sString":"Sabberworm\CSS\Value\CSSString":private]=>
 	                  string(9) "Gill Sans"
 	                }
 	                [3]=>
diff --git a/lib/Sabberworm/CSS/CSSList/CSSBlockList.php b/lib/Sabberworm/CSS/CSSList/CSSBlockList.php
index 55a594f5..0d504b0f 100644
--- a/lib/Sabberworm/CSS/CSSList/CSSBlockList.php
+++ b/lib/Sabberworm/CSS/CSSList/CSSBlockList.php
@@ -52,7 +52,7 @@ protected function allValues($oElement, &$aResult, $sSearchString = null, $bSear
 				}
 			}
 		} else {
-			//Non-List Value or String (CSS identifier)
+			//Non-List Value or CSSString (CSS identifier)
 			$aResult[] = $oElement;
 		}
 	}
diff --git a/lib/Sabberworm/CSS/Parser.php b/lib/Sabberworm/CSS/Parser.php
index c1b5ca27..6a9ca081 100644
--- a/lib/Sabberworm/CSS/Parser.php
+++ b/lib/Sabberworm/CSS/Parser.php
@@ -17,7 +17,7 @@
 use Sabberworm\CSS\Value\Size;
 use Sabberworm\CSS\Value\Color;
 use Sabberworm\CSS\Value\URL;
-use Sabberworm\CSS\Value\String;
+use Sabberworm\CSS\Value\CSSString;
 use Sabberworm\CSS\Rule\Rule;
 use Sabberworm\CSS\Parsing\UnexpectedTokenException;
 
@@ -139,7 +139,7 @@ private function parseAtRule() {
 			if ($sPrefix !== null && !is_string($sPrefix)) {
 				throw new \Exception('Wrong namespace prefix '.$sPrefix);
 			}
-			if (!($mUrl instanceof String || $mUrl instanceof URL)) {
+			if (!($mUrl instanceof CSSString || $mUrl instanceof URL)) {
 				throw new \Exception('Wrong namespace url of invalid type '.$mUrl);
 			}
 			return new CSSNamespace($mUrl, $sPrefix);
@@ -214,7 +214,7 @@ private function parseStringValue() {
 			}
 			$this->consume($sQuote);
 		}
-		return new String($sResult);
+		return new CSSString($sResult);
 	}
 
 	private function parseCharacter($bIsForIdentifier) {
diff --git a/lib/Sabberworm/CSS/Value/String.php b/lib/Sabberworm/CSS/Value/CSSString.php
similarity index 93%
rename from lib/Sabberworm/CSS/Value/String.php
rename to lib/Sabberworm/CSS/Value/CSSString.php
index c68847e5..c583efd5 100644
--- a/lib/Sabberworm/CSS/Value/String.php
+++ b/lib/Sabberworm/CSS/Value/CSSString.php
@@ -2,7 +2,7 @@
 
 namespace Sabberworm\CSS\Value;
 
-class String extends PrimitiveValue {
+class CSSString extends PrimitiveValue {
 
 	private $sString;
 
diff --git a/lib/Sabberworm/CSS/Value/URL.php b/lib/Sabberworm/CSS/Value/URL.php
index 62de1029..9ececd52 100644
--- a/lib/Sabberworm/CSS/Value/URL.php
+++ b/lib/Sabberworm/CSS/Value/URL.php
@@ -7,11 +7,11 @@ class URL extends PrimitiveValue {
 
 	private $oURL;
 
-	public function __construct(String $oURL) {
+	public function __construct(CSSString $oURL) {
 		$this->oURL = $oURL;
 	}
 
-	public function setURL(String $oURL) {
+	public function setURL(CSSString $oURL) {
 		$this->oURL = $oURL;
 	}