It's what Jeff Patton has happening after coming up with user stories. Here's an example:

User Intention	System Responsibility
	Presents user with option to add a comment to another comment.
User indicates the comment they wish to comment on.
	System prompts user for the comment.
User submits comment.
	System adds and displays comment.

Post a comment in response:

From:

Anonymous (will be screened)

OpenID (will be screened if not validated)

Dreamwidth account

If you don't have an account you can create one now.

Subject

HTML doesn't work in the subject.

Formatting type

Message