This works (i.e. the controller is invoked)
<tr id=<%=dom_id(content) %> data-controller="content" >
<td data-target="content.area"><%= content.text %></td>
<td><%= content.from_lang%></td>
<td><%= content.translations.size %> (<%= link_to 'add', new_content_translation_path(content) %>) </td>
<td><%= link_to 'Show', content %></td>
<td><%= link_to 'Edit', edit_content_path(content) %></td>
<td><%= link_to 'Destroy', content, method: :delete, data: { confirm: 'Are you sure?' } %></td>
</tr>
But changing the second line to this causes the controller not to be invoked.
<span data-target="content.area"<td><%= content.text %></td></span>
Does that make sense?