<h2 data-mercury='simple'>
<%= render_region :header do -%>
  Header
<% end -%>
</h2>
<section class="container">
  <%= render_region :content, tag: :article do %>
    Add content here
  <% end %>
</section>

<h2 id='header' data-mercury='simple'>
<%= render_region :header do -%>
  Header
<% end -%>
</h2>
<section id='content' class="container">
  <%= render_region :content, tag: :article do %>
    Add content here
  <% end %>
</section>

Add ids to default template in install generator
Add ids to default template in install generator