Trix fully supports file attachments and image attachments, as documented in the readme. It includes an inline caption editor for images.
Trix also supports "content attachments" (currently undocumented) which allow embedding arbitrary HTML as attachments in the document. Basecamp 3 uses this feature to embed @mentions with avatars, and various oEmbed types, in messages and comments.
Trix also supports "content attachments" (currently undocumented) which allow embedding arbitrary HTML as attachments in the document. Basecamp 3 uses this feature to embed @mentions with avatars, and various oEmbed types, in messages and comments.