# Default Expression

A `default` expression specifies a fallback selected during materialization when no explicit value exists.

```dcdl
port = Int default 8080;
```

`default` is not a constraint.
See [Constraints and Defaults](../constraints-and-defaults.md) for details.

## Evaluation

The fallback expression is evaluated only if materialization requires it.
When an explicit value exists, the `default` is neither evaluated nor selected.