Example: Incoming text/html + plain

Let's say you want to save the following text/html content in a richtext field:

<b>this is the body text</b>

Additionally, let's say you also want to create a plain alternative of the text/html content. You then use the following Rich Text JSON:

{
  "type": "text/html",
  "encoding": "PLAIN",
  "content": "<b>this is the body text</b>",
  "createAdditional": "plain"
}

This saves a multipart/alternative MIME:

MIME-Version: 1.0
Content-Type: multipart/alternative; 
  boundary="XXXXboundary text"
--XXXXboundary text
Content-Type: text/html

<b>this is the body text</b>
--XXXXboundary text
Content-Type: text/plain

this is the body text
--XXXXboundary text--