In addition to modules with human readable names, the schema compiler also generates modules of the form Capnp.ById.X<schema id>. These are used internally by generated code, so that generated modules with dependencies on other schema don't have to know what the human-readable names of those schema are -- they import by id.

Each module in this heirarchy just re-exports everthing from the module with a human-readable name.

This hierarchy is an implementation detail that most users don't need to know about.