Xpath search for username?

Given the XML file shown below, is there a way that I can write an xpath query that will search if a particular username exists?  Say 'jglazer"?   Should be case insensitive.

Thanks!

<Users>
  <User>
    <UserName>jglazer</UserName>
      </User>
  <User>
    <UserName>hiram</UserName>
      </User>
</Users>

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