Curly braces are used instead of square brackets in hash literals, and the key value pairs are joined by =>. A hash with a single key/value pair of Bob/84, for example, might look like this: "Bob" => 84. By separating key/value pairs with commas, further key/value pairs can be added to the hash literal.
nested-hash. Hash-ref and hash-set variations that work with nested hash tables, i.e. a hash table inside a hash table.