The term “Segmentation of the Timeline” describes both a data structure and a step in the build process, which translates the structures of the high-level-Model into a corresponding graph of Render Nodes. The latter is also known as the low-level-Model and can be seen as a set of preconfigured render pipelines. When such a pipeline is “pulled”. the render computations are invoked. The access points to all these pipelines are hooked into a backbone data structure, designated as the Fixture — which breaks down each top-level Timeline into a sequence of temporal segments: what differentiates these segments is the topology of the Render Nodes in the pipeline; whenever a change in this topology is necessary, a new segment is started. Such a change might e.g. be caused by a transition between two clips, which has to cover a range of some frames.
As of 2025, this part of the model is only roughly drafted, mostly using placeholder code to achieve some level of functional integration.
Detailed design planning and explanations can be found in the DevWiki: Segmentation.