How does IIS URL Rewrite handle # anchor tags

Question

I'm struggling to find any information on how best to handle URLs with anchor tags, like the #foo in www.example.com/index.html#foo

Our current situation is trying to use a Rewrite map for a URL with an anchor tag, but it is being trumped by another Rewrite mapping.

e.g.

 <add key="index.html#foo" value="bar1.html" />
 <add key="index.html" value="bar2.html" />

 <!-- A request to index.html#foo is being redirected to bar2.html, 
      not bar1.html as expected -->

Does URL Rewrite include this in the URL? Or is available via one of the variables? Is there documentation on this?

(I've also tried searching on "fragment identifier", "#" "hash" "hash tag")