Forking a document

[davidbrochart]

In pycrdt I'm experimenting with schema to validate incoming changes, by first applying the changes to a "twin" document of the "real" document, and if the "twin" document is still valid then the changes are applied to the "real" document.
This is expensive because data and operations are duplicated. I'm wondering if it would be possible to "fork" a document, but without data duplication. The forked document would be in a state where one could apply changes but no event change would be emitted. Then one could either discard the forked document (and the document would remain in the state before forking), or accept the forked document (and the changes would be emitted).