The "comment" feature allows users to discuss negotiation points, ask questions and provide clarifications right beside the document in a running thread:

To leave a comment, hover cursor (or on a phone, tap) beside any contract section and click the dialogue bubble icon that appears.  Note that commenting is only available in the full contract (not Overview):

Others shared on the contract will receive notifications via email when a comment is made, and again when it is "resolved."  Anyone may resolve a comment by opening the comment thread and clicking "resolve":

The comment thread is not part of the final legal document, and disappears when a comment is marked as "resolved," but a record of the conversation is maintained.