Merging XML in PHP using SimpleXML and DOM

class UserPreferences
{
        const DEFAULT_STRING = "<preferences/>";
 
        $m_preferences = null;
 
        public function __construct()
        {
                $this->m_preferences = new SimpleXMLElement(self::DEFAULT_STRING);
        }
 
        // $new is a SimpleXMLElement containing the preferences to be merged
        public function merge($new)
        {
		$mergedDom = new DOMDocument();
		$mergedDom->loadXML(self::DEFAULT_STRING);
 
		$oldDom = new DOMDocument();
		$oldDom->loadXML($this->m_preferences->asXML());
 
		// Compare existing/old preferences with the new ones.
		// If a new preference matches an old, discard the old
		// (as it is superseded by the new).
		// A match means the old and new match in node name, 				// attribute names and attribute values.
		foreach ($new->children() as $newChildName => $newChildValue)
		{
			$matchName = false;
			$matchAllAttrs = true;
			$i = 0;
 
			foreach ($this->m_preferences->children() as $oldChildName => $oldChildValue)
			{
				if ($newChildName == $oldChildName)
				{
					$matchName = true;
 
					if (count($newChildValue->attributes()) == count($oldChildValue->attributes()))
					{
						foreach ($newChildValue->attributes() as $newChildAttrName => $newChildAttrValue)
						{
							$matchAttrs = false;
 
							foreach ($oldChildValue->attributes() as $oldChildAttrName => $oldChildAttrValue)
							{
								if (($newChildAttrName == $oldChildAttrName) &&
									((string)$newChildAttrValue == (string)$oldChildAttrValue))
								{
									$matchAttrs = true;
									break;
								}
							}
 
							if (!$matchAttrs)
							{
								$matchAllAttrs = false;
								break;
							}
						}
					}
					else
					{
						$matchAllAttrs = false;
					}
				}
 
				if ($matchName && $matchAllAttrs)
				{
					// Discard the old preference.
					$oldDom->documentElement->removeChild($oldDom->documentElement->childNodes->item($i));
					$i--;
				}
 
				$i++;
			}
 
			// Merge the new preference.
			$df = $mergedDom->createDocumentFragment();
			$df->appendXML($newChildValue->asXML());
 
			$mergedDom->documentElement->appendChild($df);
		}
 
		// All new preferences are merged, and any old
		// preferences that matched any new preferences
		// have been discarded, so simply merge the remaining
		// old preferences.
		$old = simplexml_import_dom($oldDom);
 
		foreach ($old->children() as $oldChildValue)
		{
			$df = $mergedDom->createDocumentFragment();
			$df->appendXML($oldChildValue->asXML());
 
			$mergedDom->documentElement->appendChild($df);
		}
 
		// Save the result of the merge.
		$this->m_preferences = simplexml_import_dom($mergedDom);
	}
}

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class UserPreferences
{
        const DEFAULT_STRING = "<preferences/>";
 
        $m_preferences = null;
 
        public function __construct()
        {
                $this->m_preferences = new SimpleXMLElement(self::DEFAULT_STRING);
        }
 
        // $newPreferences is a SimpleXMLElement containing the preferences to be merged
	protected function _merge($newPreferences)
	{
		$mergedPreferencesDom = new DOMDocument();
		$mergedPreferencesDom->loadXML(self::DEFAULT_STRING);
 
		$oldPreferences = $this->m_preferences;
 
                // Compare existing/old preferences with the new ones.
                // If a new preference matches an old, we'll skip
                // copying the old (as it is superseded by the new).
                // A match means the old and new match in node name,
                // attribute names and attribute values.
                // (Also note that all preferences are assumed to reside
                // directly under the root <preferences> node.)
		foreach ($oldPreferences->children() as $oldPreferenceName => $oldPreference)
		{
			$found = false;
 
			foreach ($newPreferences->children() as $newPreferenceName => $newPreference)
			{
				if ($newPreferenceName == $oldPreferenceName)
				{
					if ((count($newPreference->attributes()) > 0) && (count($oldPreference->attributes()) > 0))
					{
						if (count($newPreference->attributes()) == count($oldPreference->attributes()))
						{
							$foundAllAttrs = true;
 
							foreach ($oldPreference->attributes() as $oldPreferenceAttrName => $oldPreferenceAttr)
							{
								$foundAttr = false;
 
								foreach ($newPreference->attributes() as $newPreferenceAttrName => $newPreferenceAttr)
								{
									if (($newPreferenceAttrName == $oldPreferenceAttrName) &&
										((string)$newPreferenceAttr == (string)$oldPreferenceAttr))
									{
										$foundAttr = true;
										break;
									}
								}
 
								if (!$foundAttr)
								{
									$foundAllAttrs = false;
									break;
								}
							}
 
							$found = $foundAllAttrs;
						}
					}
					else
					{
						$found = true;
					}
				}
 
				if ($found) { break; }
			}
 
			if (!$found)
			{
                                // No match, copy the old preference.
				$df = $mergedPreferencesDom->createDocumentFragment();
				$df->appendXML($oldPreference->asXML());
 
				$mergedPreferencesDom->documentElement->appendChild($df);
			}
		}
 
                // Merge/Copy all new preferences.
		foreach ($newPreferences->children() as $newPreference)
		{
			$df = $mergedPreferencesDom->createDocumentFragment();
			$df->appendXML($newPreference->asXML());
 
			$mergedPreferencesDom->documentElement->appendChild($df);
		}
 
                // Save the merged preferences.
		$this->m_preferences = simplexml_import_dom($mergedPreferencesDom);
	}

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