All four demos, stored in directories numbered from 1 to 4, use the scenes and the ProceduralWorld.gd file you can find in the Shared directory.
The ProceduralWorld class is a virtual base class that all world generators extend. It defines a _generate_sector() function that we use to generate areas of the world around the player.
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There is no such class and file
https://github.com/GDQuest/godot-procedural-generation/blob/master/godot/SpaceInfiniteGeneration/README.md#how-it-works