[BUGFIX] Correctly import nodes with different owner document

src/Sanitizer.php

@@ -184,8 +184,11 @@ protected function replaceNode(DOMNode $source, ?DOMNode $target): ?DOMNode
         if ($target === null) {
             $source->parentNode->removeChild($source);
         } elseif ($source !== $target) {
-            if ($source->ownerDocument !== $target->ownerDocument) {
-                $source->ownerDocument->importNode($target);
+            if ($source->ownerDocument !== $target->ownerDocument
+                && $source->ownerDocument !== null
+                && $target->ownerDocument !== null
+            ) {
+                $target = $source->ownerDocument->importNode($target, true);
             }
             $source->parentNode->replaceChild($target, $source);
         }

src/Visitor/CommonVisitor.php

@@ -114,8 +114,8 @@ public function leaveNode(DOMNode $domNode): ?DOMNode
         if (!$domNode instanceof DOMElement) {
             return $domNode;
         }
-        $tag = $this->behavior->getTag($domNode->nodeName);
-        if ($tag === null) {
+        $node = $this->behavior->getNode($domNode->nodeName);
+        if ($node === null) {
             // pass custom elements, in case it has been declared
             if ($this->behavior->shallAllowCustomElements() && $this->isCustomElement($domNode)) {
                 return $domNode;
@@ -124,7 +124,10 @@ public function leaveNode(DOMNode $domNode): ?DOMNode
             return null;
         }
         // completely remove node, in case it is expected to exist with children only
-        if (!$this->hasNonEmptyChildren($domNode) && $tag->shallPurgeWithoutChildren()) {
+        if ($node instanceof Behavior\Tag
+            && $node->shallPurgeWithoutChildren()
+            && !$this->hasNonEmptyChildren($domNode)
+        ) {
             return null;
         }
         return $domNode;

tests/ScenarioTest.php

@@ -226,6 +226,42 @@ public function tagIsHandled(Behavior\NodeHandler $nodeHandler, string $payload,
         self::assertSame($expectation, $sanitizer->sanitize($payload));
     }
 
+    /**
+     * @test
+     */
+    public function tagHandlingIsDelegated(): void
+    {
+        $behavior = (new Behavior())
+            ->withFlags(Behavior::REMOVE_UNEXPECTED_CHILDREN)
+            ->withName('scenario-test')
+            ->withTags(new Behavior\Tag('div', Behavior\Tag::ALLOW_CHILDREN))
+            ->withNodes(
+                new Behavior\NodeHandler(
+                    new Behavior\Tag('my-placeholder'),
+                    new Behavior\Handler\ClosureHandler(
+                        static function (NodeInterface $node, ?DOMNode $domNode): ?\DOMNode {
+                            if ($domNode === null) {
+                                return null;
+                            }
+                            $newDocument = new \DOMDocument();
+                            $text = $newDocument->createTextNode($domNode->textContent);
+                            $span = $newDocument->createElement('div');
+                            $span->setAttribute('class', 'delegated');
+                            $span->appendChild($text);
+                            return $span;
+                        }
+                    )
+                )
+            );
+        $sanitizer = new Sanitizer(
+            $behavior,
+            new CommonVisitor($behavior)
+        );
+        $payload = '<div><my-placeholder><span class="inner">value</span></my-placeholder></div>';
+        $expectation = '<div><div class="delegated">value</div></div>';
+        self::assertSame($expectation, $sanitizer->sanitize($payload));
+    }
+
     public static function commentsAreHandledDataProvider(): array
     {
         return [