Fixed ownerDocument issue with TemplateElement

lib/DOM/Document.php

@@ -67,6 +67,15 @@ class Document extends \DOMDocument {
                 $e = parent::createElement($name, $value);
             } else {
                 $e = new TemplateElement($name, $value);
+
+                // Elements that are created by their constructor in PHP aren't owned by any
+                // document and are readonly until owned by one. Temporarily append to a
+                // document fragment so the element will be owned by the document.
+                $frag = $this->createDocumentFragment();
+                $frag->appendChild($e);
+                $frag->removeChild($e);
+                unset($frag);
+
                 $this->templateElements[] = $e;
                 $e->content = $this->createDocumentFragment();
             }
@@ -88,6 +97,15 @@ class Document extends \DOMDocument {
                 $e = parent::createElementNS($namespaceURI, $qualifiedName, $value);
             } else {
                 $e = new TemplateElement($qualifiedName, $value);
+
+                // Elements that are created by their constructor in PHP aren't owned by any
+                // document and are readonly until owned by one. Temporarily append to a
+                // document fragment so the element will be owned by the document.
+                $frag = $this->createDocumentFragment();
+                $frag->appendChild($e);
+                $frag->removeChild($e);
+                unset($frag);
+
                 $this->templateElements[] = $e;
                 $e->content = $this->createDocumentFragment();
             }