media property
Media is whether the transport renders an ATTACHMENT natively. False everywhere, and a send is not refused for it: renderText flattens each attachment to one kind: url (mime) line after the text rather than dropping it. A transport whose egress hands its door the raw text would drop the attachment instead, and an attachment-only send would reach the platform with nothing to say — which is why the flag and the flattening are pinned together.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
bool? media;