<tidy-select> Columns to nest, specified
using name-variable pairs of the form new_col = c(col1, col2, col3).
The right hand side can be any valid tidy select expression.
.names_sep
If NULL, the default, the inner names will come from
the former outer names. If a string, the new inner names will use the
outer names with names_sep automatically stripped. This makes
names_sep roughly symmetric between nesting and unnesting.