Code Reference A collection of code for my reference (and perhaps other people too)

Adding Multiple Namespaces to an XDocument/XElement

Lets say you want 3 namespaces added to your document.
You would define each one with the XNamespace property:

XNamespace defaultNS = "urn://xml.voodoo.net/vd/vd-1.0";
XNamespace a = "urn://xml.voodoo.net/vd/activity-1.0";
XNamespace f = "urn://xml.voodoo.net/vd/formating-1.0";

One of the namespaces will be your default.
When you create your rood element, you first add the default and then the other after.
The other 2 are added as you see below:

XElement rootElement = new XElement(defaultNS + "root",
   new XAttribute(XNamespace.Xmlns + "f", f.NamespaceName),
   new XAttribute(XNamespace.Xmlns + "a", a.NamespaceName));

To access the other namespaces, you

XElement somethingElement = new XElement(a + "something");
somethingElement.Value = "stuff and more stuff";
rootElement.Add(somethingElement);

The result will look like this:

<root xmlns:f="urn://xml.voodoo.net/vd/formating-1.0" xmlns:a="urn://xml.voodoo.net/vd/activity-1.0" xmlns="urn://xml.voodoo.net/vd/vd-1.0">
      <a:something>stuff and more stuff</a:something>
</root>