[DotNetDevelopment] XML and namespaces

[cmt]

Hi,

I have a large XML file that uses a namespace and an XSD file to
validate with.

It validates fine, but now I need to add about 20 custom elements to
it along with a custom XSD file(no namespace on this one).

How would I "tell" the XML file that these 20 custom elements need to
validate against my custom XSD file?

So it would look something like this:

<xml>
    <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
      xsi:schemaLocation="http://ns.mystuff.org/ myxsd.xsd"
      xmlns="http://ns.mystuf.org";>
            <e1>
            <e2>
            <e3>
                 <e3a>
                 <e3b>
           </e3>
           <e4>
           <customStuff>      <-----this element is in the myxsd.xsd
file, but the child elements are not
                   <c1>
                   <c2>
                   <c3>
           </customStuff>
      </root>

Everytime I add it, and then validate it, it says "element <c1> not
allowed under "customStuff".

How can I add a custom XSD to define the elements between
<customStuff /> ?

Thanks!