module Regexp::Scanner

def self.validation_error(type, what, reason)
  case type
  when :group
    error = InvalidGroupError.new(what, reason)
  when :backref
    error = InvalidBackrefError.new(what, reason)
  when :sequence
    error = InvalidSequenceError.new(what, reason)
  else
    error = ValidationError.new('expression')
  end
  raise error # unless @@config.validation_ignore
end