Use createElementNS when creating bare elements

This forces coercion in more situations, but has the advantage of being
consistent with creating an element in the HTML namespace

lib/DOM/Document.php

@@ -76,7 +76,7 @@ class Document extends \DOMDocument {
 
         try {
             if ($name !== 'template') {
-                $e = parent::createElement($name, $value);
+                $e = parent::createElementNS(null, $name, $value);
             } else {
                 $e = new TemplateElement($this, $name, $value);
                 $this->templateElements[] = $e;
@@ -90,7 +90,7 @@ class Document extends \DOMDocument {
             //   uppercase hexadecimal digits of the character's code point
             $this->mangledElements = true;
             $name = $this->coerceName($name);
-            return parent::createElement($name, $value);
+            return parent::createElementNS(null, $name, $value);
         }
     }
 

tests/cases/TestDOM.php

@@ -44,4 +44,21 @@ class TestDOM extends \PHPUnit\Framework\TestCase {
             ["http://www.w3.org/1998/Math/MathML", "TEST",           "http://www.w3.org/1998/Math/MathML", "TEST",            ""],
         ];
     }
+    /** @dataProvider provideBareElements */
+    public function testCreateBareElements(string $nameIn, $nameOut): void {
+        $d = new Document;
+        $e = $d->createElement($nameIn);
+        $this->assertNull($e->namespaceURI);
+        $this->assertSame("", $e->prefix);
+        $this->assertSame($nameOut, $e->localName);
+    }
+
+    public function provideBareElements(): iterable {
+        return [
+            ["test",      "test"],
+            ["test:test", "testU00003Atest"],
+            ["9",         "U000039"],
+            ["TEST",      "test"],
+        ];
+    }
 }