Motivation and deployment of consensus rule changes ([soft/hard]forks).

Set out the different kinds of change to Bitcoin's rules and proposed how each kind should be rolled out.

Discussions of rule changes often led to confusion and delays. This document sorted them into types, such as accidental splits, soft forks that tighten the rules, and hard forks that need every user to upgrade, and suggested a deployment path for each. It is a guide, not a rule change.