irb(main):001:0> require 'rexml/document'
=> true
irb(main):002:0> include REXML
=> Object
irb(main):003:0> d = Document.new(File.new('/home/codemac/.hnb'))
=> <UNDEFINED> ... </>
irb(main):004:0> puts d
NoMethodError: undefined method `unpack' for nil:NilClass
        from /usr/lib/ruby/1.8/rexml/encodings/US-ASCII.rb:5:in `encode'
        from /usr/lib/ruby/1.8/rexml/output.rb:17:in `<<'
        from /usr/lib/ruby/1.8/rexml/instruction.rb:46:in `write'
        from /usr/lib/ruby/1.8/rexml/document.rb:165:in `write'
        from /usr/lib/ruby/1.8/rexml/document.rb:163:in `write'
        from /usr/lib/ruby/1.8/rexml/node.rb:23:in `to_s'
        from (irb):4
irb(main):005:0>