that are visible to `kubectl` users and API consumers, and metrics visible to cluster administrators.
Requests to a deprecated API are returned with a warning containing a target removal release and any replacement API.

    /** The key of the configuration. e.g. [a-zA-Z0-9_]+ */
    String USER_CODE_PATTERN = "user.code.pattern";

    /** The key of the configuration. e.g. Administrator */
    String MAIL_FROM_NAME = "mail.from.name";

    /** The key of the configuration. e.g. root@localhost */
    String MAIL_FROM_ADDRESS = "mail.from.address";