The copy expression allows the copy SOP node to evaluates its input graph multiple times, and vary its result each time.


## Description

It takes 2 or 3 arguments

`copy(input_index_or_node_path, default_value, attribute_name)`

- `input_index_or_node_path` is a number or a string
- `default_value` is a number
- `attribute_name` is the attribute that will be stamped

## Usage

- `copy('../copy1', 0, 'i')` - returns the index of each evaluation
- `copy('../copy1', 0)` - returns the index of each evaluation
- `copy('../copy1')` - returns the index of each evaluation
- `copy('../copy1', 0, 'id')` - returns the value of the 'id' attribute of the instance point, or 0 if the attribute doesn't exist