a single message string or a messages object where each key is an error code and corresponding message string as value.
The object is the same as the messages used as an option in any.validate().
The strings can be plain messages or a message template.
if true, turns any error generated by the ruleset to warnings.
if true, the rules will not be replaced by the same unique rule later.
For example,
Joi.number().min(1).rule({ keep: true }).min(2)will keep bothmin()rules instead of the later rule overriding the first.false