A configured metafield definition validation.
For example, for a metafield definition of `number_integer` type, you can set a validation with the name `max`
and a value of `15`. This validation will ensure that the value of the metafield is a number less than or equal to 15.
Refer to the [list of supported validations](https://shopify.dev/api/admin/graphql/reference/common-objects/metafieldDefinitionTypes#examples-Fetch_all_metafield_definition_types).