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A general description is here.
All builds have support for 'https:' URLs in 'download.file()', 'url()' and code making use of them.
Unfortunately that cannot guarantee that any particular 'https:' URL can be accessed. For example, server and client have to negotiate a cryptographic protocol (TLS, SSL, ...) and the server's identity has to be verifiable _via_ the available certificates.
The data frame and formula methods for 'aggregate()' gain a 'drop' argument.
'available.packages()' gains a 'repos' argument.