New retrieve a token representing the current revision of a document. At a later point in time, new cursors and ranges can be created and translated to the current revision from a specified previous revision.

For example, this enables:
- threaded programs can create cursors and ranges based on text they have received but which might have been changed by the user at the time they are to be created.

- editors can go accurately to the line,col position of a compilation error by saving a revision token for the last compilation.