# Type modifiers are optional, `unique` is the default.

``` ucm :hide
scratch/main> builtins.merge
```

Types and abilities may be prefixed with either `unique` or `structural`. When left unspecified, `unique` is assumed.

``` unison
type Abc = Abc
unique type Def = Def
structural type Ghi = Ghi

ability MyAbility where const : a
unique ability MyAbilityU where const : a
structural ability MyAbilityS where const : a
```