The architecture is remarkable. The lengths they’ve gone to for language version compatibility, and protecting app namespaces is especially impressive.

https://github.com/elixir-lang/expert/blob/main/pages/archit...

What are namespaces in Elixir?

Namespaces aren't so much a concept in Elixir, but this refers to the names used for things like modules. Expert will rewrite the code of its "engine" so that the engine's code and dependencies and those of the application it is embedded into don't overlap.