Fix merge method logic

README.md

@@ -212,7 +212,7 @@ Also updates the underlying object based on the new xml.
 
 #### Merge a new xml into the existing one
 
-You can easily merge a new xml into the existing one just after a provided tag name.
+You can easily merge a new xml into the existing one. It sets it as child of the provided tag.
 
 ```php
 $mapper->mergeXML($newXml, 'desiredParentTag');

src/XMLMapper.php

@@ -413,10 +413,8 @@ public function findAllAttributesOfWhere($tag, $where, $obj = null)
      */
     public function mergeXML($xml, $intoTag)
     {
-        $toMerge = new static($xml);
-        // Set tag name to "merged"
-        $toMerge->replaceTagName(['xml' => 'merged']);
-        $xml = $toMerge->getXml();
+        // remove xml tag declaration if any
+        $xml = preg_replace('/<\?xml.*?>/', '', $xml);
 
         $endTag = '</' . $intoTag . '>';
         $long = strlen($endTag);

tests/XMLMapperTest.php

@@ -306,7 +306,7 @@ public function replate_tag_name()
     public function merge_xmls()
     {
         $first = $this->loadXML();
-        $second = '<xml id="33"><content att="something"><first><second><extras><extra name="f" id="2" company="acne"></extra><extra name="edujugon" id="1" company="acne"></extra></extras></second></first></content></xml>';
+        $second = '<?xml id="33"?><content att="something"><first><second><extras><extra name="f" id="2" company="acne"></extra><extra name="edujugon" id="1" company="acne"></extra></extras></second></first></content>';
 
         $this->mapper->loadXML($first);