class Nokogiri::CSS::XPathVisitor

def css_class(hay, needle)
  if @builtins == BuiltinsConfig::ALWAYS || (@builtins == BuiltinsConfig::OPTIMAL && Nokogiri.uses_libxml?)
    # use the builtin implementation
    "nokogiri-builtin:css-class(#{hay},'#{needle}')"
  else
    # use only ordinary xpath functions
    "contains(concat(' ',normalize-space(#{hay}),' '),' #{needle} ')"
  end
end