diff --git a/CHANGELOG.md b/CHANGELOG.md
index 891adc8af..b08c38a28 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Added
 
+- Add Interface `CSSElement` (#1231)
 - Methods `getLineNumber` and `getColumnNumber` which return a nullable `int`
   for the following classes:
   `Comment`, `CSSList`, `SourceException`, `Charset`, `CSSNamespace`, `Import`,
@@ -16,12 +17,20 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 ### Changed
 
+- Parameters for `getAllValues()` are deconflated, so it now takes three (all
+  optional), allowing `$element` and `$ruleSearchPattern` to be specified
+  separately (#1241)
 - Implement `Positionable` in the following CSS item classes:
   `Comment`, `CSSList`, `SourceException`, `Charset`, `CSSNamespace`, `Import`,
   `Rule`, `DeclarationBlock`, `RuleSet`, `CSSFunction`, `Value` (#1225)
 
 ### Deprecated
 
+- Passing a string as the first argument to `getAllValues()` is deprecated;
+  the search pattern should now be passed as the second argument (#1241)
+- Passing a Boolean as the second argument to `getAllValues()` is deprecated;
+  the flag for searching in function arguments should now be passed as the third
+  argument (#1241)
 - `getLineNo()` is deprecated in these classes (use `getLineNumber()` instead):
   `Comment`, `CSSList`, `SourceException`, `Charset`, `CSSNamespace`, `Import`,
   `Rule`, `DeclarationBlock`, `RuleSet`, `CSSFunction`, `Value` (#1225, #1233)
diff --git a/src/CSSElement.php b/src/CSSElement.php
new file mode 100644
index 000000000..944aabe2c
--- /dev/null
+++ b/src/CSSElement.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS;
+
+/**
+ * Represents any entity in the CSS that is encapsulated by a class.
+ *
+ * Its primary purpose is to provide a type for use with `Document::getAllValues()`
+ * when a subset of values from a particular part of the document is required.
+ *
+ * Thus, elements which don't contain `Value`s (such as statement at-rules) don't need to implement this.
+ *
+ * It extends `Renderable` because every element is renderable.
+ */
+interface CSSElement extends Renderable {}
diff --git a/src/CSSList/CSSBlockList.php b/src/CSSList/CSSBlockList.php
index fce7913eb..aa0c67fcd 100644
--- a/src/CSSList/CSSBlockList.php
+++ b/src/CSSList/CSSBlockList.php
@@ -2,6 +2,7 @@
 
 namespace Sabberworm\CSS\CSSList;
 
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\Property\Selector;
 use Sabberworm\CSS\Rule\Rule;
 use Sabberworm\CSS\RuleSet\DeclarationBlock;
@@ -59,7 +60,53 @@ protected function allRuleSets(array &$aResult)
     }
 
     /**
-     * @param CSSList|Rule|RuleSet|Value $oElement
+     * Returns all `Value` objects found recursively in `Rule`s in the tree.
+     *
+     * @param CSSElement|string|null $element
+     *        This is the `CSSList` or `RuleSet` to start the search from (defaults to the whole document).
+     *        If a string is given, it is used as a rule name filter.
+     *        Passing a string for this parameter is deprecated in version 8.9.0, and will not work from v9.0;
+     *        use the following parameter to pass a rule name filter instead.
+     * @param string|bool|null $ruleSearchPatternOrSearchInFunctionArguments
+     *        This allows filtering rules by property name
+     *        (e.g. if "color" is passed, only `Value`s from `color` properties will be returned,
+     *        or if "font-" is provided, `Value`s from all font rules, like `font-size`, and including `font` itself,
+     *        will be returned).
+     *        If a Boolean is provided, it is treated as the `$searchInFunctionArguments` argument.
+     *        Passing a Boolean for this parameter is deprecated in version 8.9.0, and will not work from v9.0;
+     *        use the `$searchInFunctionArguments` parameter instead.
+     * @param bool $searchInFunctionArguments whether to also return Value objects used as Function arguments.
+     *
+     * @return array<int, Value>
+     *
+     * @see RuleSet->getRules()
+     */
+    public function getAllValues(
+        $element = null,
+        $ruleSearchPatternOrSearchInFunctionArguments = null,
+        $searchInFunctionArguments = false
+    ) {
+        if (\is_bool($ruleSearchPatternOrSearchInFunctionArguments)) {
+            $searchInFunctionArguments = $ruleSearchPatternOrSearchInFunctionArguments;
+            $searchString = null;
+        } else {
+            $searchString = $ruleSearchPatternOrSearchInFunctionArguments;
+        }
+
+        if ($element === null) {
+            $element = $this;
+        } elseif (\is_string($element)) {
+            $searchString = $element;
+            $element = $this;
+        }
+
+        $result = [];
+        $this->allValues($element, $result, $searchString, $searchInFunctionArguments);
+        return $result;
+    }
+
+    /**
+     * @param CSSElement|string $oElement
      * @param array<int, Value> $aResult
      * @param string|null $sSearchString
      * @param bool $bSearchInFunctionArguments
diff --git a/src/CSSList/CSSList.php b/src/CSSList/CSSList.php
index 2156aa111..18d926e15 100644
--- a/src/CSSList/CSSList.php
+++ b/src/CSSList/CSSList.php
@@ -4,6 +4,7 @@
 
 use Sabberworm\CSS\Comment\Comment;
 use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\OutputFormat;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Parsing\SourceException;
@@ -31,7 +32,7 @@
  *
  * It can also contain `Import` and `Charset` objects stemming from at-rules.
  */
-abstract class CSSList implements Commentable, Positionable, Renderable
+abstract class CSSList implements Commentable, CSSElement, Positionable
 {
     use Position;
 
diff --git a/src/CSSList/Document.php b/src/CSSList/Document.php
index f74c89645..ed4b09b38 100644
--- a/src/CSSList/Document.php
+++ b/src/CSSList/Document.php
@@ -8,7 +8,6 @@
 use Sabberworm\CSS\Property\Selector;
 use Sabberworm\CSS\RuleSet\DeclarationBlock;
 use Sabberworm\CSS\RuleSet\RuleSet;
-use Sabberworm\CSS\Value\Value;
 
 /**
  * This class represents the root of a parsed CSS file. It contains all top-level CSS contents: mostly declaration
@@ -77,33 +76,6 @@ public function getAllRuleSets()
         return $aResult;
     }
 
-    /**
-     * Returns all `Value` objects found recursively in `Rule`s in the tree.
-     *
-     * @param CSSList|RuleSet|string $mElement
-     *        the `CSSList` or `RuleSet` to start the search from (defaults to the whole document).
-     *        If a string is given, it is used as rule name filter.
-     * @param bool $bSearchInFunctionArguments whether to also return Value objects used as Function arguments.
-     *
-     * @return array<int, Value>
-     *
-     * @see RuleSet->getRules()
-     */
-    public function getAllValues($mElement = null, $bSearchInFunctionArguments = false)
-    {
-        $sSearchString = null;
-        if ($mElement === null) {
-            $mElement = $this;
-        } elseif (is_string($mElement)) {
-            $sSearchString = $mElement;
-            $mElement = $this;
-        }
-        /** @var array<int, Value> $aResult */
-        $aResult = [];
-        $this->allValues($mElement, $aResult, $sSearchString, $bSearchInFunctionArguments);
-        return $aResult;
-    }
-
     /**
      * Returns all `Selector` objects with the requested specificity found recursively in the tree.
      *
diff --git a/src/Rule/Rule.php b/src/Rule/Rule.php
index e358d93f4..a34018a84 100644
--- a/src/Rule/Rule.php
+++ b/src/Rule/Rule.php
@@ -4,13 +4,13 @@
 
 use Sabberworm\CSS\Comment\Comment;
 use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\OutputFormat;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Parsing\UnexpectedEOFException;
 use Sabberworm\CSS\Parsing\UnexpectedTokenException;
 use Sabberworm\CSS\Position\Position;
 use Sabberworm\CSS\Position\Positionable;
-use Sabberworm\CSS\Renderable;
 use Sabberworm\CSS\Value\RuleValueList;
 use Sabberworm\CSS\Value\Value;
 
@@ -19,7 +19,7 @@
  *
  * In CSS, `Rule`s are expressed as follows: “key: value[0][0] value[0][1], value[1][0] value[1][1];”
  */
-class Rule implements Commentable, Positionable, Renderable
+class Rule implements Commentable, CSSElement, Positionable
 {
     use Position;
 
diff --git a/src/RuleSet/RuleSet.php b/src/RuleSet/RuleSet.php
index 85b94f263..12b8157ac 100644
--- a/src/RuleSet/RuleSet.php
+++ b/src/RuleSet/RuleSet.php
@@ -4,6 +4,7 @@
 
 use Sabberworm\CSS\Comment\Comment;
 use Sabberworm\CSS\Comment\Commentable;
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\OutputFormat;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Parsing\UnexpectedEOFException;
@@ -22,7 +23,7 @@
  * If you want to manipulate a `RuleSet`, use the methods `addRule(Rule $rule)`, `getRules()` and `removeRule($rule)`
  * (which accepts either a `Rule` or a rule name; optionally suffixed by a dash to remove all related rules).
  */
-abstract class RuleSet implements Commentable, Positionable, Renderable
+abstract class RuleSet implements CSSElement, Commentable, Positionable
 {
     use Position;
 
diff --git a/src/Value/Value.php b/src/Value/Value.php
index beb74464a..3025566f0 100644
--- a/src/Value/Value.php
+++ b/src/Value/Value.php
@@ -2,19 +2,19 @@
 
 namespace Sabberworm\CSS\Value;
 
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Parsing\SourceException;
 use Sabberworm\CSS\Parsing\UnexpectedEOFException;
 use Sabberworm\CSS\Parsing\UnexpectedTokenException;
 use Sabberworm\CSS\Position\Position;
 use Sabberworm\CSS\Position\Positionable;
-use Sabberworm\CSS\Renderable;
 
 /**
  * Abstract base class for specific classes of CSS values: `Size`, `Color`, `CSSString` and `URL`, and another
  * abstract subclass `ValueList`.
  */
-abstract class Value implements Positionable, Renderable
+abstract class Value implements CSSElement, Positionable
 {
     use Position;
 
diff --git a/tests/Unit/CSSList/CSSBlockListTest.php b/tests/Unit/CSSList/CSSBlockListTest.php
new file mode 100644
index 000000000..85a2e9e75
--- /dev/null
+++ b/tests/Unit/CSSList/CSSBlockListTest.php
@@ -0,0 +1,279 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\CSSList\AtRuleBlockList;
+use Sabberworm\CSS\Rule\Rule;
+use Sabberworm\CSS\RuleSet\DeclarationBlock;
+use Sabberworm\CSS\Tests\Unit\CSSList\Fixtures\ConcreteCSSBlockList;
+use Sabberworm\CSS\Value\CSSFunction;
+use Sabberworm\CSS\Value\CSSString;
+use Sabberworm\CSS\Value\Size;
+
+/**
+ * @covers \Sabberworm\CSS\CSSList\CSSBlockList
+ */
+final class CSSBlockListTest extends TestCase
+{
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWhenNoContentSetReturnsEmptyArray()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        self::assertSame([], $subject->getAllValues());
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesReturnsOneValueDirectlySetAsContent()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value = new CSSString('Superfont');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule = new Rule('font-family');
+        $rule->setValue($value);
+        $declarationBlock->addRule($rule);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues();
+
+        self::assertSame([$value], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesReturnsMultipleValuesDirectlySetAsContentInOneDeclarationBlock()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new CSSString('Superfont');
+        $value2 = new CSSString('aquamarine');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule1 = new Rule('font-family');
+        $rule1->setValue($value1);
+        $declarationBlock->addRule($rule1);
+        $rule2 = new Rule('color');
+        $rule2->setValue($value2);
+        $declarationBlock->addRule($rule2);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues();
+
+        self::assertSame([$value1, $value2], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesReturnsMultipleValuesDirectlySetAsContentInMultipleDeclarationBlocks()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new CSSString('Superfont');
+        $value2 = new CSSString('aquamarine');
+
+        $declarationBlock1 = new DeclarationBlock();
+        $rule1 = new Rule('font-family');
+        $rule1->setValue($value1);
+        $declarationBlock1->addRule($rule1);
+        $declarationBlock2 = new DeclarationBlock();
+        $rule2 = new Rule('color');
+        $rule2->setValue($value2);
+        $declarationBlock2->addRule($rule2);
+        $subject->setContents([$declarationBlock1, $declarationBlock2]);
+
+        $result = $subject->getAllValues();
+
+        self::assertSame([$value1, $value2], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesReturnsValuesWithinAtRuleBlockList()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value = new CSSString('Superfont');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule = new Rule('font-family');
+        $rule->setValue($value);
+        $declarationBlock->addRule($rule);
+        $atRuleBlockList = new AtRuleBlockList('media');
+        $atRuleBlockList->setContents([$declarationBlock]);
+        $subject->setContents([$atRuleBlockList]);
+
+        $result = $subject->getAllValues();
+
+        self::assertSame([$value], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWithElementProvidedReturnsOnlyValuesWithinThatElement()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new CSSString('Superfont');
+        $value2 = new CSSString('aquamarine');
+
+        $declarationBlock1 = new DeclarationBlock();
+        $rule1 = new Rule('font-family');
+        $rule1->setValue($value1);
+        $declarationBlock1->addRule($rule1);
+        $declarationBlock2 = new DeclarationBlock();
+        $rule2 = new Rule('color');
+        $rule2->setValue($value2);
+        $declarationBlock2->addRule($rule2);
+        $subject->setContents([$declarationBlock1, $declarationBlock2]);
+
+        $result = $subject->getAllValues($declarationBlock1);
+
+        self::assertSame([$value1], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWithSearchStringProvidedReturnsOnlyValuesFromMatchingRules()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new CSSString('Superfont');
+        $value2 = new CSSString('aquamarine');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule1 = new Rule('font-family');
+        $rule1->setValue($value1);
+        $declarationBlock->addRule($rule1);
+        $rule2 = new Rule('color');
+        $rule2->setValue($value2);
+        $declarationBlock->addRule($rule2);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues('font-');
+
+        self::assertSame([$value1], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWithSearchStringProvidedInNewMethodSignatureReturnsOnlyValuesFromMatchingRules()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new CSSString('Superfont');
+        $value2 = new CSSString('aquamarine');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule1 = new Rule('font-family');
+        $rule1->setValue($value1);
+        $declarationBlock->addRule($rule1);
+        $rule2 = new Rule('color');
+        $rule2->setValue($value2);
+        $declarationBlock->addRule($rule2);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues(null, 'font-');
+
+        self::assertSame([$value1], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesByDefaultDoesNotReturnValuesInFunctionArguments()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new Size(10, 'px');
+        $value2 = new Size(2, '%');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule = new Rule('margin');
+        $rule->setValue(new CSSFunction('max', [$value1, $value2]));
+        $declarationBlock->addRule($rule);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues();
+
+        self::assertSame([], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWithSearchInFunctionArgumentsReturnsValuesInFunctionArguments()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new Size(10, 'px');
+        $value2 = new Size(2, '%');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule = new Rule('margin');
+        $rule->setValue(new CSSFunction('max', [$value1, $value2]));
+        $declarationBlock->addRule($rule);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues(null, true);
+
+        self::assertSame([$value1, $value2], $result);
+    }
+
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function getAllValuesWithSearchInFunctionArgumentsInNewMethodSignatureReturnsValuesInFunctionArguments()
+    {
+        $subject = new ConcreteCSSBlockList();
+
+        $value1 = new Size(10, 'px');
+        $value2 = new Size(2, '%');
+
+        $declarationBlock = new DeclarationBlock();
+        $rule = new Rule('margin');
+        $rule->setValue(new CSSFunction('max', [$value1, $value2]));
+        $declarationBlock->addRule($rule);
+        $subject->setContents([$declarationBlock]);
+
+        $result = $subject->getAllValues(null, null, true);
+
+        self::assertSame([$value1, $value2], $result);
+    }
+}
diff --git a/tests/Unit/CSSList/CSSListTest.php b/tests/Unit/CSSList/CSSListTest.php
new file mode 100644
index 000000000..d7fa79cba
--- /dev/null
+++ b/tests/Unit/CSSList/CSSListTest.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\CSSElement;
+use Sabberworm\CSS\Tests\Unit\CSSList\Fixtures\ConcreteCSSList;
+
+/**
+ * @covers \Sabberworm\CSS\CSSList\CSSList
+ */
+final class CSSListTest extends TestCase
+{
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function implementsCSSElement()
+    {
+        $subject = new ConcreteCSSList();
+
+        self::assertInstanceOf(CSSElement::class, $subject);
+    }
+}
diff --git a/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php b/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php
new file mode 100644
index 000000000..574fef2d9
--- /dev/null
+++ b/tests/Unit/CSSList/Fixtures/ConcreteCSSBlockList.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList\Fixtures;
+
+use Sabberworm\CSS\CSSList\CSSBlockList;
+use Sabberworm\CSS\OutputFormat;
+
+final class ConcreteCSSBlockList extends CSSBlockList
+{
+    /**
+     * @return never
+     */
+    public function isRootList()
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395831);
+    }
+
+    /**
+     * @param OutputFormat|null $outputFormat
+     *
+     * @return never
+     */
+    public function render($outputFormat)
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395836);
+    }
+}
diff --git a/tests/Unit/CSSList/Fixtures/ConcreteCSSList.php b/tests/Unit/CSSList/Fixtures/ConcreteCSSList.php
new file mode 100644
index 000000000..ec00ce6f6
--- /dev/null
+++ b/tests/Unit/CSSList/Fixtures/ConcreteCSSList.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\CSSList\Fixtures;
+
+use Sabberworm\CSS\CSSList\CSSList;
+use Sabberworm\CSS\OutputFormat;
+
+final class ConcreteCSSList extends CSSList
+{
+    /**
+     * @return never
+     */
+    public function isRootList()
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395831);
+    }
+
+    /**
+     * @param OutputFormat|null $outputFormat
+     *
+     * @return never
+     */
+    public function render($outputFormat)
+    {
+        throw new \BadMethodCallException('Not implemented', 1740395836);
+    }
+}
diff --git a/tests/Unit/Rule/RuleTest.php b/tests/Unit/Rule/RuleTest.php
index 0364e1eae..8a2f0e6d4 100644
--- a/tests/Unit/Rule/RuleTest.php
+++ b/tests/Unit/Rule/RuleTest.php
@@ -3,6 +3,7 @@
 namespace Sabberworm\CSS\Tests\Unit\Rule;
 
 use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\CSSElement;
 use Sabberworm\CSS\Parsing\ParserState;
 use Sabberworm\CSS\Settings;
 use Sabberworm\CSS\Rule\Rule;
@@ -15,6 +16,18 @@
  */
 final class RuleTest extends TestCase
 {
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function implementsCSSElement()
+    {
+        $subject = new Rule('beverage-container');
+
+        self::assertInstanceOf(CSSElement::class, $subject);
+    }
+
     /**
      * @return array<string, array{0: string, 1: list<class-string>}>
      */
diff --git a/tests/Unit/RuleSet/Fixtures/ConcreteRuleSet.php b/tests/Unit/RuleSet/Fixtures/ConcreteRuleSet.php
new file mode 100644
index 000000000..0aa966699
--- /dev/null
+++ b/tests/Unit/RuleSet/Fixtures/ConcreteRuleSet.php
@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\RuleSet\Fixtures;
+
+use Sabberworm\CSS\OutputFormat;
+use Sabberworm\CSS\RuleSet\RuleSet;
+
+final class ConcreteRuleSet extends RuleSet
+{
+    /**
+     * @param OutputFormat|null $outputFormat
+     *
+     * @return never
+     */
+    public function render($outputFormat)
+    {
+        throw new \BadMethodCallException('Nothing to see here :/', 1744067015);
+    }
+}
diff --git a/tests/Unit/RuleSet/RuleSetTest.php b/tests/Unit/RuleSet/RuleSetTest.php
new file mode 100644
index 000000000..d5231e1fb
--- /dev/null
+++ b/tests/Unit/RuleSet/RuleSetTest.php
@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\RuleSet;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\CSSElement;
+use Sabberworm\CSS\Tests\Unit\RuleSet\Fixtures\ConcreteRuleSet;
+
+/**
+ * @covers \Sabberworm\CSS\RuleSet\RuleSet
+ */
+final class RuleSetTest extends TestCase
+{
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function implementsCSSElement()
+    {
+        $subject = new ConcreteRuleSet();
+
+        self::assertInstanceOf(CSSElement::class, $subject);
+    }
+}
diff --git a/tests/Unit/Value/Fixtures/ConcreteValue.php b/tests/Unit/Value/Fixtures/ConcreteValue.php
new file mode 100644
index 000000000..e47e2da5e
--- /dev/null
+++ b/tests/Unit/Value/Fixtures/ConcreteValue.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\Value\Fixtures;
+
+use Sabberworm\CSS\OutputFormat;
+use Sabberworm\CSS\Value\Value;
+
+final class ConcreteValue extends Value
+{
+    /**
+     * @param OutputFormat|null $outputFormat
+     *
+     * @return never
+     */
+    public function render($outputFormat)
+    {
+        throw new \BadMethodCallException('Nothing to see here :/', 1744067951);
+    }
+
+    /**
+     * @return string
+     */
+    public function __toString()
+    {
+        return $this->render(new OutputFormat());
+    }
+}
diff --git a/tests/Unit/Value/ValueTest.php b/tests/Unit/Value/ValueTest.php
new file mode 100644
index 000000000..d9ce5a4f3
--- /dev/null
+++ b/tests/Unit/Value/ValueTest.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sabberworm\CSS\Tests\Unit\Value;
+
+use PHPUnit\Framework\TestCase;
+use Sabberworm\CSS\CSSElement;
+use Sabberworm\CSS\Tests\Unit\Value\Fixtures\ConcreteValue;
+use Sabberworm\CSS\Value\Value;
+
+/**
+ * @covers \Sabberworm\CSS\Value\Value
+ */
+final class ValueTest extends TestCase
+{
+    /**
+     * @test
+     *
+     * @return void
+     */
+    public function implementsCSSElement()
+    {
+        $subject = new ConcreteValue();
+
+        self::assertInstanceOf(CSSElement::class, $subject);
+    }
+}