diff --git a/src/CSSList/CSSBlockList.php b/src/CSSList/CSSBlockList.php
index 8c58fbf9..4db38bfa 100644
--- a/src/CSSList/CSSBlockList.php
+++ b/src/CSSList/CSSBlockList.php
@@ -140,4 +140,27 @@ protected function allSelectors(array &$aResult, $sSpecificitySearch = null)
             }
         }
     }
+
+    /**
+     * @param CSSList|Rule|RuleSet|Value $oElement
+     * @param array<int, CSSFunction> $aResult
+     *
+     * @return void
+     */
+    protected function allFunctions($oElement, array &$aResult)
+    {
+        if ($oElement instanceof CSSBlockList) {
+            foreach ($oElement->getContents() as $oContent) {
+                $this->allFunctions($oContent, $aResult);
+            }
+        } elseif ($oElement instanceof RuleSet) {
+            foreach ($oElement->getRules() as $oRule) {
+                $this->allFunctions($oRule, $aResult);
+            }
+        } elseif ($oElement instanceof Rule) {
+            $this->allFunctions($oElement->getValue(), $aResult);
+        } elseif ($oElement instanceof CSSFunction) {
+            $aResult[] = $oElement;
+        }
+    }
 }
diff --git a/src/CSSList/Document.php b/src/CSSList/Document.php
index 822f3995..1ae31d01 100644
--- a/src/CSSList/Document.php
+++ b/src/CSSList/Document.php
@@ -109,6 +109,26 @@ public function getSelectorsBySpecificity($sSpecificitySearch = null)
         return $aResult;
     }
 
+    /**
+     * Returns all `CSSFunction` objects recursively found in the tree, no matter how deeply nested the rule sets are.
+     * 
+     * @param CSSList|RuleSet|string $mElement
+     *        the `CSSList` or `RuleSet` to start the search from (defaults to the whole document).
+     *        If a string is given, it is used as rule name filter.
+     *
+     * @return array<int, CSSFunction>
+     */
+    public function getAllFunctions($mElement = null)
+    {
+        if ($mElement === null) {
+            $mElement = $this;
+        }
+        /** @var array<int, Value> $aResult */
+        $aResult = [];
+        $this->allFunctions($mElement, $aResult);
+        return $aResult;
+    }
+
     /**
      * Expands all shorthand properties to their long value.
      *
diff --git a/src/Value/Size.php b/src/Value/Size.php
index 8fd92f13..18466f05 100644
--- a/src/Value/Size.php
+++ b/src/Value/Size.php
@@ -23,6 +23,7 @@ class Size extends PrimitiveValue
         'vh', 'dvh', 'svh', 'lvh',
         'vw', 'vmin', 'vmax', 'rem',
         'svw', 'lvw', 'dvw',
+        'x', 'dppx', 'dpi', 'dpcm',
     ];
 
     /**
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index 965376d0..8f1422a7 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -1325,4 +1325,19 @@ public function escapedSpecialCaseTokens(): void
         self::assertTrue(\is_a($urlRule->getValue(), '\\Sabberworm\\CSS\\Value\\URL'));
         self::assertTrue(\is_a($calcRule->getValue(), '\\Sabberworm\\CSS\\Value\\CalcFunction'));
     }
+
+    /**
+     * @test
+     */
+    public function imagesetInFile(): void
+    {
+        $oDoc = self::parsedStructureForFile('image-set', Settings::create()->withMultibyteSupport(true));
+        $sExpected = sprintf(
+            '%s%s%s',
+            '.home_banner {background-image: image-set(url("https://www.example.us/images/home-banner.webp") 1x,',
+            'url("https://www.example.us/images/home-banner@2x.webp") 2x,',
+            'url("https://www.example.us/images/home-banner@3x.webp") 3x);}'
+        );
+        self::assertSame($sExpected, $oDoc->render());
+    }
 }
diff --git a/tests/fixtures/image-set.css b/tests/fixtures/image-set.css
new file mode 100644
index 00000000..17e3d606
--- /dev/null
+++ b/tests/fixtures/image-set.css
@@ -0,0 +1 @@
+.home_banner{background-image: image-set(url(https://www.example.us/images/home-banner.webp) 1x,url(https://www.example.us/images/home-banner@2x.webp) 2x,url(https://www.example.us/images/home-banner@3x.webp) 3x);}
\ No newline at end of file