I'm working with libxml and I can't seem to define a subclass of
XML::Document. For example,

require 'libxml'

class SubDocument < XML::Document
  def initialize(name)
    super
    @sub_name = name
  end

  def sub_method
    puts "the method"
  end
end

> s = SubDocument.new('test')
=> <?xml version="test"?>

> s.respond_to? 'sub_method'
=> false

> s.class
=> XML::Document

As you can see from the above, it's as if I'm aliasing XML::Document,
rather than subclassing it. I have also tried including XML and then
defining the subclass as well as opening the XML module and then
defining the subclass -- same results in both cases. I've never come
across this before. Is there a way to fix this or should I just write
my class to contain an XML::Document?

Thanks,
Jeremy