Design Google Docs

Design Google Docs. Multiple people edit the same document at once and see each other's changes and cursors in near real time. Documents are persisted with revision history, can be edited offline, and carry sharing permissions and comments.

In scope: the concurrent edit model (operational transform or CRDT), session routing and ownership, operation log and snapshots, presence, offline reconciliation, permissions and anchored comments. Out of scope: rich-text rendering and the file storage hierarchy of a drive.