Assign arg to the struct member of corresponding type. Note: It's compile-time error to assign parameter of type which is not part of WriteOptions.
Exact mode. Save all comments and empty lines as is.
Pretty mode. Save comments, skip existing new lines, add line before the next group.
Whether to write empty line after each group except for the last. New line is not written when it already exists before the next group.
Whether to preserve comments (lines that starts with '#') on saving.
Whether to preserve empty lines on saving.
Behavior of ini-like file saving.