Checks if a predictor expression is additive or not
Usage
bru_is_additive(x, ...)
# S3 method for class 'data.frame'
bru_is_additive(x, root_id = 0, ..., verbose = FALSE)
# S3 method for class 'character'
bru_is_additive(x, ...)
# S3 method for class 'expression'
bru_is_additive(x, ...)
# S3 method for class 'formula'
bru_is_additive(x, ...)