More explanation for how to generate crossed and nested data structure with the interaction term

[hallegue]

In Section 2.1.3, there is an example of how to generate crossed and nested data structure using the interaction term (with the : symbol). This needs more explanation to understand how this method relates the classic method of using the / symbol.

Here's the section part in question:

We can also output the crossed and nested using :

make_structure(structure="treatment(2) + individual(5) + treatment:individual", repeat_obs=1)