Separate values with a boundary

The boundary parameter and delimiter lines must agree; a delimiter MUST NOT occur inside a part.

• The media type is multipart/form-data and its boundary parameter is required. The format is transport-independent; the browser and receiving web application here are one example, not the only possible users.
• Each part has headers, an empty line, then its data. Delimiter lines use two leading hyphens and the boundary value. CRLF means the two bytes carriage return and line feed.
• The delimiter after the final part has two extra trailing hyphens. A delimiter between parts does not close the body. RFC 2046 section 5.1.1 supplies this MIME framing; verified erratum 4676 corrects the misplaced hyphens in RFC 7578 section 4.6.
• The delimiter MUST NOT appear inside an encapsulated part. Choose a different boundary if it would collide. Boundary values can need quoting. Construct each delimiter by adding two hyphens to the actual parameter value, even if that value itself starts with hyphens.
• The worked boundary Picnic is a short fictional fixture. MIME boundary values are limited to 70 characters excluding the two delimiter hyphens. No HTTP method, request length or transport security is specified by this body format.

The drawing labels empty lines and CRLF for explanation; those labels are not transmitted text. The bounded teaching encoder accepts a conservative ASCII boundary/header subset, emits exact bytes, and rejects delimiter-prefix collisions. It is not a streaming MIME parser or a browser form implementation.