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P4 CLI Documentation | 2025.2

# The mainline model

The mainline model of software configuration management defines a stream hierarchy The set of parent-to-child relationships between streams in a stream depot. based on the stability of the contents of the stream, from less stable to most stable.

`release` and `sparserel` codelines are the most stable. The `mainline` codeline is fairly stable. For example, the code must build. `development` and `sparsedev` codelines are less stable. |

### Propagate change between streams

The principle of change propagation is merge down, copy up. The goal is to keep less stable streams up to date with their more stable parent or child, so that when change is propagated from a less stable stream to a more stable one, no work is overwritten. This approach keeps the resolve operation as simple as possible. The merge/copy and resolve features allow you to propagate change between streams.

If you want to merge or copy between peer streams (for example, to merge another developer's changes to your development stream), you must first reparent your stream. To reparent a stream, edit the stream specification and change the Parent field. This approach is a key benefit of streams: the ability to configure the flow of change.

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