Embryo/Http/Message/Traits/HeadersTrait.php
protected function setHeaderName(string $key)
        {
            $key = strtr(strtolower($key), '_', '-');
            if (strpos($key, 'http-') === 0) {
                $key = substr($key, 5);
            }
            return $key;
        }
protected function setHeaderName(string $key)
        {
            $key = strtr(strtolower($key), '_', '-');
            if (strpos($key, 'http-') === 0) {
                $key = substr($key, 5);
            }
            return $key;
        }
protected function setHeaderName ( string $ key ) { $ key = strtr ( strtolower ( $ key ) , '_' , '-' ) ; if ( strpos ( $ key , 'http-' ) === 0 ) { $ key = substr ( $ key , 5 ) ; } return $ key ; }
Sets case-insensitive header name.

@param string $key
@return string
Sets case - insensitive header name .