use alias types

Author: l-trotta

specification/_types/Retriever.ts

@@ -22,7 +22,7 @@ import { Sort, SortResults } from '@_types/sort'
 import { FieldCollapse } from '@global/search/_types/FieldCollapse'
 import { Rescore } from '@global/search/_types/rescoring'
 import { UserDefinedValue } from '@spec_utils/UserDefinedValue'
-import { Id } from './common'
+import {Id, IndexName} from './common'
 import { QueryContainer } from './query_dsl/abstractions'
 
 /**
@@ -91,8 +91,8 @@ export enum ScoreNormalizer {
 }
 
 export class SpecifiedDocument {
-  index?: string
-  id: string
+  index?: IndexName
+  id: Id
 }
 
 export class StandardRetriever extends RetrieverBase {