multixml_comparison.rb

require 'multi_xml'
require 'pp'

xml = <<-EOF
<atom:feed xmlns="http://kosapi.feld.cvut.cz/schema/3" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:osearch="http://a9.com/-/spec/opensearch/1.1/" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:base="https://kosapi.fit.cvut.cz/api/3" xml:lang="cs">
  <atom:link atom:rel="next" href="courses?offset=10&amp;limit=10"/>
  <osearch:startIndex>0</osearch:startIndex>
</atom:feed>
EOF

[:rexml, :nokogiri, :libxml, :ox].each do |impl|
  puts "#### #{impl}"
  MultiXml.parser = impl
  pp MultiXml.parse(xml)
end

result.rb

#### rexml
{"feed"=>
  {"xmlns"=>"http://kosapi.feld.cvut.cz/schema/3",
   "xmlns:atom"=>"http://www.w3.org/2005/Atom",
   "xmlns:osearch"=>"http://a9.com/-/spec/opensearch/1.1/",
   "xmlns:xlink"=>"http://www.w3.org/1999/xlink",
   "xmlns:xsi"=>"http://www.w3.org/2001/XMLSchema-instance",
   "xml:base"=>"https://kosapi.fit.cvut.cz/api/3",
   "xml:lang"=>"cs",
   "link"=>{"atom:rel"=>"next", "href"=>"courses?offset=10&limit=10"},
   "startIndex"=>"0"}}
#### nokogiri
{"feed"=>
  {"link"=>{"rel"=>"next", "href"=>"courses?offset=10&limit=10"},
   "startIndex"=>"0",
   "base"=>"https://kosapi.fit.cvut.cz/api/3",
   "lang"=>"cs"}}
#### libxml
{"feed"=>
  {"link"=>{"rel"=>"next", "href"=>"courses?offset=10&limit=10"},
   "startIndex"=>"0",
   "base"=>"https://kosapi.fit.cvut.cz/api/3",
   "lang"=>"cs"}}
#### ox
{"atom:feed"=>
  {"xmlns"=>"http://kosapi.feld.cvut.cz/schema/3",
   "xmlns:atom"=>"http://www.w3.org/2005/Atom",
   "xmlns:osearch"=>"http://a9.com/-/spec/opensearch/1.1/",
   "xmlns:xlink"=>"http://www.w3.org/1999/xlink",
   "xmlns:xsi"=>"http://www.w3.org/2001/XMLSchema-instance",
   "xml:base"=>"https://kosapi.fit.cvut.cz/api/3",
   "xml:lang"=>"cs",
   "atom:link"=>{"atom:rel"=>"next", "href"=>"courses?offset=10&limit=10"},
   "osearch:startIndex"=>"0"}}