A container object for populated argument values.

The following are all valid examples:

• { }
• { foo: 1 }
• { foo: true }
• { foo: 'bar' }
• { foo: [ 1, 2 ] }
• { foo: [ true, true ] }
• { foo: [ 'bar', 'gar' ] }
• { foo: { a: 1 } }
• { foo: { a: { b: 'c'} } }
• { foo: [ { a: { b: 'c'} }, { a: { b: 'c'} } ] }

An array of arrays is not allowed, so the following is an INVALID example:

• { foo: [ [ 1, 2 ], [3, 4 ] ] }