[kazinator]

If you export your contacts in one e-mail program and import it into another, the import and export functions are kinds of APIs, but the exported format isn't.

The interchange format becomes an API if you encode requests in it. Along that axis, it can become a programming language that defines a new API.

If the interchange data does nothing beyond storing a representation of itself, which is then operated upon by some procedures not specified in that data itself, then it's not an API.