Nested interface definition in Angular

I have an interface with a complex type as a member like this.

export interface Activity {
  id: string;
  name: string;
  segment: Segment;
}

export interface Segment {
  id: string;
  name: string;
}

I'm used to C# and nested classes so somewhere in my spine I feel that this might be improved so that the structure of the segment is inside the activity. I'm not sure what it's called so I failed finding/recognized adequate examples.

Is t even possible in TypeScript/Angular? I'm not sure I've even seen an import to such a nested type ever-ever. In case it's possible, what are the disadvantages/caveats (except the obvious complexity of the interfaces)? In case it's not a feasible choice relying on interfaces, are classes or types something that would be?

Proof of effort.

• This on presents a structure without the names of the internal entity.
• This one has corresponding structure but no answer.
• This one turned out to be totally unrelated despite the title.
• This one is weirdly downvoted for unclear reason.
• This one touches the right spots but lack an apparent answer to my issue.
• This one is way overkill and I still can't recognize my particular need.

You can use namespace for that:

export interface Activity {
  id: string;
  name: string;
  segment: Activity.Segment;
}

export namespace Activity {
  export interface Segment {
    id: string;
    name: string;
  }
}