The function extracts how many times each level of an attribute should occur within the design when attribute level balance is not enforced. Note that it extracts the parentheses AFTER the end of the square brackets. Specifying round brackets without the square brackets are syntactically invalid and therefore we want the code to fail in this case.
extract_level_occurrence(string, simplify = FALSE)
A character string
If TRUE return as a vector. Default is FALSE.