The number of missing values, either 1, 2, or 3. (This is, unusually,
a single byte instead of a 32-bit number.)
-@itemx long_string_missing_value values[];
+@item long_string_missing_value values[];
The missing values themselves. This array contains exactly
@code{n_missing_values} elements, each of which has the following
substructure:
missing values are allowed to be non-spaces, and any spaces within the
first 8 bytes are included in the missing value here.
-@itemx char value[];
+@item char value[];
The missing value string, exactly @code{value_len} bytes, without
any padding or null terminator.
@end table