A tarball is a file that contains an archive of a directory or file(s) created by the command tar (which stands for tape archive). It's commonly used in Unix-like systems and they are often compressed with gzip or bzip2.
[insert history and reason for the name "tarball"]
Tcl supports tar filesystems with the vfs::tar module of the tclvfs. What would the code look like to access a tar file from Tcl, using tclvfs, and accounting for the possible compression of the file?