@Override
    protected void formatMultipartHeader(
        final MultipartPart part,
        final OutputStream out) throws IOException {

        // For strict, we output all fields with MIME-standard encoding.
        final Header header = part.getHeader();
        for (final MimeField field: header) {
            writeField(field, out);
        }
    }
Constructs a new instance of {@code HttpStrictMultipart} with the given charset, boundary, parts, preamble, and epilogue.

@param charset the charset to use.
@param boundary the boundary string to use.
@param parts the list of parts to include in the multipart message.
@param preamble the preamble string to use.
@param epilogue the epilogue string to use.
httpclient5/src/main/java/org/apache/hc/client5/http/entity/mime/HttpStrictMultipart.java