Communication within the context of your book is done by placing requests to your peers in the comments.
Make a selection on your book either with a search or by selecting a single transaction and open the Activity Sidebar.
Comments refer to the context they are created in.
Refer to a @username to notify people on the book.
Save your comment.
Team members are notified in App.
And by Email.
Click on the comment to get in its context.
After clicking on the comment you get to the initial context.
Working within the context of a comment has proven to save a lot of time on communication between peers.