src/Primitive/Support/Traits/RetrievableTrait.php
protected function getGrammar()
    {
        return [
            'true' => true, 'false' => false,
            'on' => true,   'off' => false,
            'yes' => true,  'no' => false,
            'y' => true,    'n' => false,
            '+' => true,    '-' => false
        ];
    }
protected function getGrammar()
    {
        return [
            'true' => true, 'false' => false,
            'on' => true,   'off' => false,
            'yes' => true,  'no' => false,
            'y' => true,    'n' => false,
            '+' => true,    '-' => false
        ];
    }
Return grammar to construct Bool from string.

@return array