Limits of Backbone.Model.previousAttributes for Rolling Back a Failed save()

Rollback goal

I want to restore a Backbone model's client-side state after model.save() fails, using the documented previousAttributes() snapshot and the model's error event. The intent is a clean revert without triggering view re-renders, so the plan is to reapply the snapshot with the silent option.

Constraints and uncertainty

The model holds nested objects and arrays as attribute values. My understanding is that previousAttributes() returns a shallow snapshot, so nested references may already reflect the failed edits, making the revert incomplete. I am also unsure how far back the snapshot reaches: whether it reflects state before the last set or before the last successful sync, and how multiple unsaved changes interact with it.

Assume Backbone 1.x. Server-side effects of a partially processed request are out of scope; the concern is only local attribute consistency.

Questions

• Does previousAttributes() capture state from the last set call or the last successful save, and what happens across several unsaved mutations?
• Is a manual deep copy before save() the only reliable way to roll back nested attributes?
• Does reapplying the snapshot with {silent: true} fully suppress change events, or are there edge cases?