This package provides a testing release for upcoming LaTeX2e
kernel changes. Testing by the LaTeX team itself suggests that
the code is stable and usable, but wider use by knowledgeable
users is required by adding these changes to the release LaTeX
kernel. Typically, the code here will be used by a TeX system
to create dedicated formats, for example pdflatex-dev, which
can then be used explicitly for testing.

Homepage:
https://ctan.org/pkg/latex-base-dev
