src/Responder/FormattedResponder.php
protected function assertValid(array $classes)
    {
        parent::assertValid($classes);

        foreach ($classes as $formatter => $quality) {
            if (!is_subclass_of($formatter, FormatterInterface::class)) {
                throw FormatterException::invalidClass($formatter);
            }

            if (!is_float($quality)) {
                throw FormatterException::needsQuality($formatter);
            }
        }
    }
protected function assertValid(array $classes)
    {
        parent::assertValid($classes);

        foreach ($classes as $formatter => $quality) {
            if (!is_subclass_of($formatter, FormatterInterface::class)) {
                throw FormatterException::invalidClass($formatter);
            }

            if (!is_float($quality)) {
                throw FormatterException::needsQuality($formatter);
            }
        }
    }
@inheritDoc

@throws FormatterException
If $classes does not implement the correct interface,
or does not have a quality value.