title: In Open Graph markup, what's the use of 'og:locale:alternate' without the location (href)?
body: <p>Facebook's Open Graph Protocol markup <a href="http://ogp.me/#optional" rel="noreferrer">allows for defining</a> the current web page's locale, and any alternative locales it's also available in, using a markup like this:</p>
  
  <pre><code>&lt;meta property="og:locale" content="en_GB"&gt;
  &lt;meta property="og:locale:alternate" content="fr_FR"&gt;
  &lt;meta property="og:locale:alternate" content="es_ES"&gt;
  </code></pre>
  
  <p>The current page's permalink can be easily deduced (from the URL, Canonical URL meta tag, or <code>og:url</code>).</p>
  
  <p>But what's the point of including <code>og:locale:alternate</code> without their respective URLs? How is it at all useful?</p>