Creates a code block.
code_block(fun, next_elt = TRUE)Function to execute within code block.
This function's argument list must include ....
It may also include any of the following named arguments:
state, the participant's state object;
opt, which is the test's option list as created by test_options();
input, the current page's Shiny input object;
output, the current page's Shiny output object;
session, the current Shiny session object;
elts, the timeline (i.e. list of test elements).
(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).