C# Online Compiler | .NET Fiddle

<no name> by Anonymous

using System;
using System.Xml.Linq;

public class Program
{
    public static void Main()
    {
        XNamespace ns = "urn:iso:std:iso:20022:tech:xsd:pain.001.001.03";

        var childNodes = new XElement(ns + "GrpHdr");
        var loadedNodes = new[]
        {
            XElement.Parse(
                @"<PmtInf xmlns=""urn:iso:std:iso:20022:tech:xsd:pain.001.001.03"">...</PmtInf>")
        };

        var content = new XElement(ns + "CstmrCdtTrfInitn", childNodes, loadedNodes);

        var document = new XElement(ns + "Document", content);

		document.Save(Console.Out, SaveOptions.None);

		Console.WriteLine();		
		
        document.Save(Console.Out, SaveOptions.OmitDuplicateNamespaces);
    }
}

​x
 
using System;
using System.Xml.Linq;
​
public class Program
{
    public static void Main()
    {
        XNamespace ns = "urn:iso:std:iso:20022:tech:xsd:pain.001.001.03";
​
        var childNodes = new XElement(ns + "GrpHdr");
        var loadedNodes = new[]
        {
            XElement.Parse(
                @"<PmtInf xmlns=""urn:iso:std:iso:20022:tech:xsd:pain.001.001.03"">...</PmtInf>")
        };
​
        var content = new XElement(ns + "CstmrCdtTrfInitn", childNodes, loadedNodes);
​
        var document = new XElement(ns + "Document", content);
​
        document.Save(Console.Out, SaveOptions.None);
​
        Console.WriteLine();        
        
        document.Save(Console.Out, SaveOptions.OmitDuplicateNamespaces);
    }
}

Roslyn 2.0 Compiler; Environment version: 4.0.30319.42000

Test serialization of a fresh intance of Fibextoobject:
<?xml version="1.0" encoding="utf-16"?>
<FIBEX xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.asam.net/xml/fbx">
  <ELEMENTS>
    <CLUSTERS>
      <CLUSTER xmlns:q1="http://www.asam.net/xml/fbx/ethernet" xsi:type="q1:CLUSTER-TYPE" ID="ID_CLUSTER_MAIN_1">
        <SHORT-NAME xmlns="http://www.asam.net/xml">SomeIpDatabase</SHORT-NAME>
        <SPEED>1000000000</SPEED>
      </CLUSTER>
    </CLUSTERS>
  </ELEMENTS>
</FIBEX>

Input XML file:
<fx:FIBEX xmlns:fx="http://www.asam.net/xml/fbx" xmlns:ho="http://www.asam.net/xml" xmlns:ethernet="http://www.asam.net/xml/fbx/ethernet" xmlns:it="http://www.asam.net/xml/fbx/it" xmlns:service="http://www.asam.net/xml/fbx/services" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="" VERSION="4.1.0">
  <fx:ELEMENTS>
    <fx:CLUSTERS>
      <fx:CLUSTER xsi:type="ethernet:CLUSTER-TYPE" ID="ID_CLUSTER_MAIN_1">
        <ho:SHORT-NAME>SomeIpDatabase</ho:SHORT-NAME>
        <fx:SPEED>1000000000</fx:SPEED>
        <fx:IS-HIGH-LOW-BIT-ORDER>false</fx:IS-HIGH-LOW-BIT-ORDER>
        <fx:BIT-COUNTING-POLICY>SAWTOOTH</fx:BIT-COUNTING-POLICY>
        <fx:PROTOCOL>ETHERNET</fx:PROTOCOL>
        <fx:PHYSICAL>OABR</fx:PHYSICAL>
        <fx:CHANNEL-REFS>
          <fx:CHANNEL-REF ID-REF="ID_CHANNEL_SOME_IP_1" />
        </fx:CHANNEL-REFS>
        <fx:MAX-FRAME-LENGTH>1500</fx:MAX-FRAME-LENGTH>
        <ethernet:MAC-MULTICAST-GROUPS>
          <ethernet:MAC-MULTICAST-GROUP ID="ID_CLUSTER_MAIN_1_ID_MACMULTICASTGROUP_SD_1">
            <ho:SHORT-NAME>SD</ho:SHORT-NAME>
            <ethernet:MAC-MULTICAST-ADDRESS>01:00:5E:40:FF:FB</ethernet:MAC-MULTICAST-ADDRESS>
          </ethernet:MAC-MULTICAST-GROUP>
          <ethernet:MAC-MULTICAST-GROUP ID="ID_CLUSTER_MAIN_1_ID_MACMULTICASTGROUP_BROADCAST_1">
            <ho:SHORT-NAME>BROADCAST</ho:SHORT-NAME>
            <ethernet:MAC-MULTICAST-ADDRESS>FF:FF:FF:FF:FF:FF</ethernet:MAC-MULTICAST-ADDRESS>
          </ethernet:MAC-MULTICAST-GROUP>
        </ethernet:MAC-MULTICAST-GROUPS>
      </fx:CLUSTER>
      
    </fx:CLUSTERS>
  </fx:ELEMENTS>
  
</fx:FIBEX>

Deserialized and re-serialized Fibextoobject
<?xml version="1.0" encoding="utf-16"?>
<FIBEX xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.asam.net/xml/fbx">
  <ELEMENTS>
    <CLUSTERS>
      <CLUSTER xmlns:q1="http://www.asam.net/xml/fbx/ethernet" xsi:type="q1:CLUSTER-TYPE" ID="ID_CLUSTER_MAIN_1">
        <SHORT-NAME xmlns="http://www.asam.net/xml">SomeIpDatabase</SHORT-NAME>
        <SPEED>1000000000</SPEED>
      </CLUSTER>
    </CLUSTERS>
  </ELEMENTS>
</FIBEX>

Cached Result
Last Run:	12:40:41 am
Compile:	0.191s
Execute:	0.119s
Memory:	2.35Mb
CPU:	0.172s

View IL Code