ID of this content. A content component in a multipart/related content group
has a unique ID property that can be used to reference the part in an
HTML part within the group.
The collection of MIME headers associated with this content.
Every content object may potentially come from MIME source regardless of
its type. Therefore along with content data and attributes there can be
arbitrary MIME headers associated with it.
Below are examples in XML formats. All examples are shown with all inherited members. Quoting when required is part of the examples, but you must obviously populate with your own data.