HTML exports created with Pluto often depend on third party resources from cdns (e.g. jsdelivr), but also from any resource the notebook may include itself (e.g. Plotly assets, external images and other multimedia files loaded over the internet or from users computer).

An HTML notebook archive would inline all these resources into a (potentially huge) HTML file that would be viewable via file:/// without any references to external resources. That way completely self-contained notebooks can be shared.