What does "lazy-loaded" means in the context of sysdata.rda file in a package?

General
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When we want to store multiple internal objects in a package, we should use a R/sysdata.rda file. The tool usethis::use_data (when using internal = TRUE) simply creates a list of the passed objects (argument ...) and stores them in such a file. I'm concerned with the loading of this R/sysdata.rda file.

The book "Writing R Extensions" states:

Two exceptions are allowed: if the R subdirectory contains a file sysdata.rda (...) this will be lazy-loaded into the namespace environment – this is intended for system datasets that are not intended to be user-accessible via data.

The book "R Packages" states:

The LazyData field in the package DESCRIPTION has no impact on R/sysdata.rda but is strictly about the exported data below data/. Internal data is always lazy-loaded.

However, internal data being lazy-loaded might mean two things:

  1. When one of the objects in that file is needed, the complete file is loaded.
  2. When one of the objects in that file is needed, only that object is loaded.

Which one of this statements is the correct one?

Thanks