I was deceived by this snippet. I expected that I would get an undefined subroutine &HTML::Entities::encode error, but in fact, it run OK and printed A http://www.nowhere.com/?action=a1&param=p1. I then took a look at the HTML::TreeBuilder source and found that HTML::Entities was indeed use'd there. I rechecked its manual, and I didn't find any result on entity, entities, decode, and encode keywords. It also might be worth to note that HTML::Entities is part of HTML-Parser distribution.