next.js/packages/next/src/server/route-matchers/app-page-route-matcher.ts

import { RouteMatcher } from './route-matcher'
import type { AppPageRouteDefinition } from '../route-definitions/app-page-route-definition'

export class AppPageRouteMatcher extends RouteMatcher<AppPageRouteDefinition> {
  public get identity(): string {
    return `${this.definition.pathname}?__nextPage=${this.definition.page}`
  }
}