When a value represents a named domain concept (e.g., Theme), use the corresponding enum type/constant (e.g., `ThemeEnum`) instead of duplicating raw string literals (`'light'`, `'dark'`). This keeps identifier naming consistent across schema definitions and UI/component logic. Example pattern: ```ts // Prefer a single source of truth export enum ThemeEnum { Light = 'light', Dark = 'dark', } // Derive schema from the enum rather than retyping literals import { z } from 'zod'; const FormSchema = z.object({ theme: z.enum([ThemeEnum.Light, ThemeEnum.Dark] as [string, string]), }); // And use enum values in UI/selectors ```