title, institution,
source, history,
references, comment, Conventions
units,
standard_name, long_name,
ancillary_variables, missing_value,
valid_range, valid_min,
valid_max, flag_values,
flag_meanings, flag_masks,
_FillValue, standard_error_multiplier
coordinates, axis,
bounds, grid_mapping,
formula_terms, calendar,
leap_month, leap_year,
month_lengths, positive
add_offset, scale_factor, compress, cell_measures,
cell_methods, climatology,
Most of these CF attributes are optional.