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A.2 Introducing Changesets

It is often extremely useful to compare two project trees (usually for the same project) and figure out exactly what has changed between them. A record of such changes is called a changeset or a delta.

Changesets are a very central concept to arch – much of arch is defined in terms of operations performed with changesets.

If you have a changeset between an "old tree" and a "new tree", you can "apply the changeset" to the old tree to get the new tree – in other words, you can automatically make the editing changes described by a changeset. If you have some third tree, you can apply the patch to get an approximation of making the same changes to that third tree.

arch includes sophisticated tools for creating and applying changesets.