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_Types ~~and~~ are Values_

# Default Values

Elements of a disjunction may be marked as preferred.
If there is only one mark, or the users constraints a field enough such that
only one mark remains, that value is the default value.

In the example, `replicas` defaults to `1`.
In the case of `protocol`, however, there are multiple definitions with
different, mutually incompatible defaults.
In that case, both `"tcp"` and `"udp"` are preferred and one must explicitly
specify either `"tcp"` or `"udp"` as if no marks were given.

<!-- CUE editor -->
_defaults.cue:_
```
// any positive number, 1 is the default
replicas: uint | *1

// the default value is ambiguous
protocol: *"tcp" | "udp"
protocol: *"udp" | "tcp"
```

<!-- result -->
`$ cue eval defaults.cue`
```
replicas: 1
protocol: "tcp" | "udp" | *_|_
```