Every HTTP::Exception is a Exception::Class - Class. So the same
mechanisms apply as with Exception::Class-classes. In fact have a look
at Exception::Class' docs for more general information on exceptions
and Exception::Class::Base for information on what methods a caught
exception also has.

HTTP::Exception is only a factory for HTTP::Exception::XXX (where X is
a number) subclasses. That means that HTTP::Exception->new(404)
returns a HTTP::Exception::404 object, which in turn is a
HTTP::Exception::Base - Object.