Send a Sample: no more txt option + trigger?

Hello,

we have just noticed the following changes on Marketo Send a Sample feature. As far as I know there is no documentation on change. Can somebody please explain?
- there is no longer the option to send a test on .txt. Do you confirm or is it automatic?
- there is now an option called "trigger". What does that mean? What does the "opportunity" option below means?

thanks!

Cécile @ Talend