This is an implementation of OT for text which implements transform property 2 through the use of tombstones. As such, this data structure can be used in peer-to-peer situations (with concurrency control algorithms which do not have a single source of truth). Documents are a string with tombstones inserted throughout. For example, 'some ', (2 tombstones), 'string'. Tombstones indicate positions where characters once existed. They are important for many parties to agree on convergence.