Hashes are great for storing named data, but if you want more than one
entry for a name, you have to use a list of pairs. Even then, this is
really boring to write:

$values = [
foo => undef,
bar => undef,
baz => undef,
xyz => { ... },
];

Just look at all those undefs! Don't worry, we can get rid of those:

$values = [
map { $_ => undef } qw(foo bar baz),
xyz => { ... },
];

Aaaauuugh! We've saved a little typing, but now it requires thought to
read, and thinking is even worse than typing.

With Data::OptList, you can do this instead:

$values = Data::OptList::mkopt([
qw(foo bar baz),
xyz => { ... },
]);

This works by assuming that any defined scalar is a name and any
reference following a name is its value.