How do I determine language of the document in Parse Filter?

[Savannah Beckett]

Hi,
  How do I determine the language of the document inside a parse filter 
function?  I am writing a my own parse filter: 


 public ParseResult filter(Content content, ParseResult parseResult,
                              HTMLMetaTags metaTags, DocumentFragment doc) 

I am trying to do "doc.get("lang")", but compiler complained it cannot find 
symfol for Get( ) function in DocumentFragment interface.  


Thanks.