src/Mail/mime.php
function encodeHeader($name, $value, $charset, $encoding)
    {
        $mime_part = new Mail_mimePart;
        return $mime_part->encodeHeader(
            $name, $value, $charset, $encoding, $this->_build_params['eol']
        );
    }
function encodeHeader($name, $value, $charset, $encoding)
    {
        $mime_part = new Mail_mimePart;
        return $mime_part->encodeHeader(
            $name, $value, $charset, $encoding, $this->_build_params['eol']
        );
    }
Encodes a header as per RFC2047

@param string $name     The header name
@param string $value    The header data to encode
@param string $charset  Character set name
@param string $encoding Encoding name (base64 or quoted-printable)

@return string          Encoded header data (without a name)
@access public
@since 1.5.3