Creates a reactive page. A reactive page is defined by a function that is called once the participant reaches a given location in the timeline. This function must be idempotent, i.e. calling it multiple times should have the same effect as calling it once).
reactive_page(fun, next_elt = TRUE)Function that returns a page argument.
This function's argument list must include ....
It should also include one or more named arguments that provide
information for generating the new page: potential arguments
include state, corresponding to the participant's
state object,
answer, which is the most recent participant response,
and opt, which is the test's option list as created by
test_options.
The function should always return an object of class page.
(Logical scalar) Whether to go to the next element
in the timeline once this page is completed.
This will typically be TRUE,
except for special cases such as pages that load
testing sessions from file (get_p_id).