Formatting a colonnade object may lead to some columns being omitted due to width restrictions. This method returns a character vector that describes each of the omitted columns.
extra_cols(x, ...) # S3 method for squeezed_colonnade extra_cols(x, ..., n = Inf)
The number of extra columns to return; the returned vector will
always contain as many elements as there are extra columns, but elements
#>  "b <int>"