returns the elements of an array joined by a separator string


## Description

It takes 1 or 2 arguments.

`join(array_or_word, separator)`

- `array_or_word` - array to join the elements of
- `separator` - string to join the elements (default is a space ' ')

## Usage

- `join([1,2])` - returns '1 2'
- `join([1,2,3],',')` - returns '1,2,3'