Confused about cookie domain/trustedOrigins

import { betterAuth } from "better-auth"
 
export const auth = betterAuth({
    advanced: {
        crossSubDomainCookies: {
            enabled: true,
            domain: "app.example.com", // your domain
        },
    },
    trustedOrigins: [
        'https://example.com',
        'https://app1.example.com',
        'https://app2.example.com',
    ],
})