In Drupal 8, rendering Tables is still a lot like Drupal 7. You build out multi-dimensional arrays of rows and columns in PHP that Drupal transforms into a <tr> and <td>s respectively. There is still this confusing Drupalism known as 'data' that lets you add render array elements as cell data (not to be confused with data attributes).

I've been given a site where the developer chose to use 'data' to render the contents of the cell, but I cannot figure out how to add a class to the <td> around the data.

I've read the source code and documentation for Table.php and I'm aware of the new #wrapper_attributes but I cannot crack this.

I've tried at least four ways to add the class, and none work.

$table['row-' . $row_id] = [

  // Option 1: Class appears on <tr> tag
  '#attributes' => [
    'class' => ['option-1-row-attributes'],
    'id' => 'row-' . $row_id,
    'no_striping' => TRUE,
  ],

  // Option 2: Class appears on <td> tag of first column. 
  'item' => [
    '#markup' => $row['my_item']->label(),
    '#wrapper_attributes' => [   
      'class' => ['option-2-markup-wrapper-attributes'],
    ],
  ],

  // In the following section, the only item that works is
  // the class on the <a> tag.
  'edit_operation' => [
    'data' => [
      '#type' => 'link',
      '#url' => Url::fromRoute('my_module.my_route', ['item' => $row_id]),
      '#title' => $this->t('Edit'),
      '#attributes' => [
        // Option 3: Class appears on the anchor tag
        'class' => ['use-ajax', 'option-3-link-attributes'],
        'data-dialog-type' => 'modal',
        'data-dialog-options' => Json::encode([
          'width' => 700,
        ]),
      ],
      // Option 4: Has no effect.
      '#wrapper_attributes' => [
        'class' => ['option-4-data-wrapper-attributes'],
      ],
    ],
    // Option 5: Update: This appears to be the correct solution! 
    // Class appears on the <td>.
    '#wrapper_attributes' => [
      'class' => ['option-5-wrapper-attributes'],
    ],
    // Option 6: Has no effect.
    '#attributes' => [
      'class' => ['option-6-attributes'],
    ],
    // Option 7: Has no effect.
    'class' => ['option-7-attributes'],
  ],
];