class Capybara::Selector::CSSBuilder

def class_conditions(classes)
  case classes
  when XPath::Expression
    raise ArgumentError, 'XPath expressions are not supported for the :class filter with CSS based selectors'
  when Regexp
    strs = Selector::RegexpDisassembler.new(classes).substrings
    strs.map { |str| "[class*='#{str}'#{' i' if classes.casefold?}]" }.join
  else
    cls = Array(classes).group_by { |cl| cl.start_with? '!' }
    (cls[false].to_a.map { |cl| ".#{Capybara::Selector::CSS.escape(cl)}" } +
    cls[true].to_a.map { |cl| ":not(.#{Capybara::Selector::CSS.escape(cl.slice(1..-1))})" }).join
  end
end