dict_col_t::is_nullable(): Determine if the column can be set NULL.

dict_col_t::is_nullable(): Determine if the column is virtual.

dict_col_t::is_instant(): Determine if the column has been instantly added.

dict_col_t::instant_value(): Get the default value of an instantly-added
column.

dict_index_t::get_n_nullable(n_prefix): Determine the number of nullable
index fields in the prefix.

dict_index_t::instant_field_value(): Get the default value of a
clustered index field of an instantly-added column.