public function validateKey(string $key)
    {
        if (false === isset($this->definitions[$key])) {
            throw new \InvalidArgumentException(sprintf(
                'Descriptor "%s" not a permitted descriptor key. Did you make a typo? Permitted descriptors: "%s"',
                $key,
                implode('", "', array_keys($this->definitions))
            ));
        }
    }
public function validateKey(string $key)
    {
        if (false === isset($this->definitions[$key])) {
            throw new \InvalidArgumentException(sprintf(
                'Descriptor "%s" not a permitted descriptor key. Did you make a typo? Permitted descriptors: "%s"',
                $key,
                implode('", "', array_keys($this->definitions))
            ));
        }
    }
public function validateKey ( string $ key ) { if ( false === isset ( $ this -> definitions [ $ key ] ) ) { throw new \ InvalidArgumentException ( sprintf ( 'Descriptor "%s" not a permitted descriptor key. Did you make a typo? Permitted descriptors: "%s"' , $ key , implode ( '", "' , array_keys ( $ this -> definitions ) ) ) ) ; } }
Ensure that a given key is valid.

This is called when the user attempts to access a descriptor.
Ensure that a given key is valid .