<div itemscope itemtype="http://schema.org/WebSite">

  <meta itemprop="url" content="https://www.example.com/"/>

  <form itemprop="potentialAction" itemscope itemtype="http://schema.org/SearchAction">

    <meta itemprop="target" content="https://query.example.com/search?q={search_term_string}"/>

    <input itemprop="query-input" type="text" name="search_term_string" required/>

    <input type="submit"/>

  </form>

</div>