Why Intellisence doesn't show up for snippettag ?

Question

I want to create a Code Snippet for VS:

<?xml version="1.0" encoding="utf-8" ?>
<CodeSnippets xmlns="http://schemas.microsoft.com/VisualStudio/2008/CodeSnippet"&gt;

  <CodeSnippet Format="1.0.0">
    <Header>
      <SnippetTypes>
      </SnippetTypes>
    </Header>
    <Snippet>

Why Intellisense doesn't show up when I typed SnippetTypes to suggest me the 3 values

* SurroundsWith
* Expansion
* Refactoring