private function addHeader ($header, $unique = FALSE)
    {

        // If the header is an array

        if (is_array ($header))
        {

            // Merge the headers arrays

            $this->_headers	= array_merge ($this->_headers, $header);

        }
        else
        {

            // If unique remove any duplicates

            if ($unique)
            {

                $headerArray	= explode (':', $header);
                $headerKey		= $headerArray[0];

                foreach ($this->_headers as $key => $val)
                {

                    if (stripos ($val, $headerKey) === 0)
                    {

                        unset ($this->_headers[$key]);

                    }

                }

            }

            // Add the header to the headers array

            $this->_headers[]	= $header;

        }

    }