Attachment elements can be dragged or copied, either alone or as part of a range, from one web view to another editable web view. While the attachments appear and are rendered correctly in the destination web view, they lack the underlying file wrappers. This can be seen by dragging an attachment from the destination web view to a Finder window. It doesn’t materialize as a file on drop.
We may want to consider dragging separately from copying, because the former allows for promises whereas the latter doesn’t.
<rdar://problem/43684573>
Wenson thinks I reported the same thing in bug 190530. *** This bug has been marked as a duplicate of bug 190530 ***