The last line of your code sample is
not XML at all. It is not well-formed and cannot be parsed.
Before working with XAML and other XML applications, you need to learn XML itself. Your problem with the syntax is very basic: you cannot add any tags in the opening tags. You only insert inner XML between opening and closing tags:
<someElement someAttribute="you cannot have XML inside the tag">
<!--
</someElement>
Please see:
http://en.wikipedia.org/wiki/XML[
^],
http://www.w3.org/TR/xml/[
^],
http://www.xml.com/axml/testaxml.htm[
^].
—SA