Entity newbie question

Hi folks,

I have a problem with this Entity.
<!-- Documents using the kimber index method must have a lang attribute
-->
<!-- Only one of these should be present in the entity -->

<!ENTITY lang 'concat(/*/@lang, /*/@xml:lang, "en")'>

Found in the html/autoidx.xsl .
What is the function of these Entity, i didn't found any wring Syntax in
my XML document. I declared an lang="en" attribute in the <book> -tag.

What's going wrong?

Greez Andreas