Questions
Ask about a specific passage, and answer in a thread.
A question is anchored to the paragraph it is about. No more "I don't get the part about the second example" — the question sits on that example.
Asking
Hover the passage and press Ask a question, or select some text and use the question button in the toolbar. Write it and send.
Students can ask even where they cannot edit: a read-only document still takes questions.
Answering
Questions appear in the course's questions panel, and a marker shows on every block that has one. Each question opens a thread — replies stay under it, anchored to the same passage.
Teachers get an email when a question is asked, and the student gets one when it is answered. Nobody has to keep the tab open.
Closing the loop
A teacher marks a thread as resolved once it is answered, so the panel shows what still needs attention.
Authors can edit or delete their own messages; teachers can moderate any of them.
Who sees what
Everyone with access to the document sees the questions and their answers — that is the point: one student's question usually answers three others. For something you want to keep to yourself, take a note instead.
A course reused in several classes shares its questions across all of them.