JOIN combines a list of values into one new value by appending them. Optionally, you can also specify a string to put in between values.
JOIN((p.first_name, p.last_name), " ")
It is common practice to have two separate information fields for a name - one for the first and one for the last name. If, once these data are collected, you want to treat the full name as one combined piece of information, you could use
JOIN in a calculated information like in the example above.
c.names_of_all_people := JOIN(get_properties(instances(Person), full_name),", ")