require 'rexml/document'
require 'open-uri'
include REXML

require 'expatparser'
REXML::Parsers.registry[:default] = REXML::Parsers.registry[:expat]

nsmap = {
  'atom'=>'http://www.w3.org/2005/Atom',
  'xhtml'=>'http://www.w3.org/1999/xhtml'
}

source = open('http://www.tbray.org/ongoing/ongoing.atom').read
doc = Document.new(source)
XPath.each(doc, '//atom:title', nsmap) do |title|
  puts title.text
end