src/Http/Header.php
public function has($key)
    {
        if (\strpos($key, '_')) {
            $key = \str_replace('_', '-', $key);
        }

        return isset($this->headerNames[\strtolower($key)]);
    }
public function has($key)
    {
        if (\strpos($key, '_')) {
            $key = \str_replace('_', '-', $key);
        }

        return isset($this->headerNames[\strtolower($key)]);
    }
public function has ( $ key ) { if ( \ strpos ( $ key , '_' ) ) { $ key = \ str_replace ( '_' , '-' , $ key ) ; } return isset ( $ this -> headerNames [ \ strtolower ( $ key ) ] ) ; }
Returns true if the HTTP header is defined.

@param string $key The HTTP header

@return bool true if the parameter exists, false otherwise
Returns true if the HTTP header is defined .