New Mail option in daily build 722

In the new mail popup option, the blog docs say:

Composing an E-mail

To send an e-mail, you pass “mail” as the first argument to the function, and pass an options table with the following (optional) fields:

to – a string for one recipient, or an array of strings for multiple recipients.
subject – a string representing the e-mail subject line.
body – a string representing the e-mail body content.
isBodyHTML – a boolean (true/false) used to toggle whether body contains HTML or not (default is false).
attachment – a table with three keys: baseDir, filename, and type (e.g. “image”).
Its the last line (attachment) I have a question about.

If I am sending a file containing text, but which I would rather people not open in a text editor, or a binary file which is not an image, what should I use for the type option? [import]uid: 108660 topic_id: 20105 reply_id: 320105[/import]

It would appear that it doesn’t matter what I use.
Maybe its just a hint for email apps to know whether they should try to show a preview? [import]uid: 108660 topic_id: 20105 reply_id: 78568[/import]