WebKit Quirks.cpp
This bit was interesting.<p><pre><code>  bool Quirks::requiresUserGestureToPauseInPictureInPicture() const
  {
  #if ENABLE(VIDEO_PRESENTATION_MODE)
      &#x2F;&#x2F; Facebook, Twitter, and Reddit will naively pause a &lt;video&gt; element that has scrolled out of the viewport,
      &#x2F;&#x2F; regardless of whether that element is currently in PiP mode.
      &#x2F;&#x2F; We should remove the quirk once &lt;rdar:&#x2F;&#x2F;problem&#x2F;67273166&gt;, &lt;rdar:&#x2F;&#x2F;problem&#x2F;73369869&gt;, and &lt;rdar:&#x2F;&#x2F;problem&#x2F;80645747&gt; have been fixed.
      if (!needsQuirks())
          return false;

      if (!m_requiresUserGestureToPauseInPictureInPicture) {
          auto domain = RegistrableDomain(m_document-&gt;topDocument().url()).string();
          m_requiresUserGestureToPauseInPictureInPicture = domain == &quot;facebook.com&quot;_s || domain == &quot;twitter.com&quot;_s || domain == &quot;reddit.com&quot;_s;
      }
  
      return *m_requiresUserGestureToPauseInPictureInPicture;
  #else
      return false;
  #endif
  }</code></pre>