All structures inherit from the Value class and so structure instances implement the Value methods print(), format(), classOf(), superClassOf(), isKindOf(), ==, and !=. The copy() method is the only method not inherited from Value that structures implement. It yields a top-level copy of the structure you call it on, meaning that you get a new, separate structure instance containing the same element values as the original and then you can modify that copy independently. The element values are not themselves copies, so for example, if one of the elements was an array, the copy would reference that same array, not a copy of that array.
Defining Local Functions in Structures
Structure Scope While Initializing