class ActiveModel::Validations::FormatValidator

def validate_each(record, attribute, value)
  if options[:with]
    regexp = option_call(record, :with)
    record_error(record, attribute, :with, value) unless regexp.match?(value.to_s)
  elsif options[:without]
    regexp = option_call(record, :without)
    record_error(record, attribute, :without, value) if regexp.match?(value.to_s)
  end
end