It's glob and/or bsd_glob from the underlying C stdlib. Another interesting example of things the stdlib glob can do:

  #!/usr/bin/perl
  # perl since it's an easy way to use an arbitrary function from stdlib
  use File::Glob "bsd_glob";
  for (bsd_glob("{Hello,Hi} {world,everyone}...a {demo,example}")) {
    print($_."\n");
  }