declare module '@mdit-vue/types' {
  interface MarkdownItEnv {
    foo?: string[];
  }
}

import MarkdownIt from 'markdown-it';
import type { MarkdownItEnv } from '@mdit-vue/types';

const md = MarkdownIt({ html: true });
const env: MarkdownItEnv = {};
const rendered = md.render('raw markdown text', env);