key property
A key is the required name of the tag. The string value can be 1-128 Unicode
characters in length and can't be prefixed with "aws:" or "dms:". The string
can only contain only the set of Unicode letters, digits, white-space, '_',
'.', '/', '=', '+', '-' (Java regular expressions:
"^(\p{L}\p{Z}\p{N}_.:/=+\-
*)$").
Implementation
final String? key;