HTML in data of theme_table() According to http://www.drupalcontrib.org/api/drupal/drupal!core!includes!theme.inc/function/theme_table/8 

I created a table in my custom page in Drupal 8.

$build = [
  'table' =&gt; [
    '#theme' =&gt; 'table',
    '#header' =&gt; $header,
    '#rows' =&gt; $rows,
  ],
];

return $build;


Example of the first row.

$row = [
    'billing' =&gt; [
    'data' =&gt; $invoice . '&lt;small&gt;' . $label . '&lt;/small&gt;',
  ],


In my page the &lt;small&gt; tag is displayed as it and not rendered as HTML tag. I tried to add attributes =&gt; ['html'] or this kind of option but it does not work.

How can I render HTML markup in theme_table()?
You can use FormattableMarkup to insert variables into html markup:

use Drupal\Component\Render\FormattableMarkup;

  'data' =&gt; new FormattableMarkup('&lt;b&gt;@bar&lt;/b&gt;', ['@bar' =&gt; $foo]);