<% content_for :title, "#{declarable.description_plain} | Trade Tariff | GOV.UK" %>

<article class="tariff commodity">
  <div class="inner">
    <nav class="trail">
      <dl>
        <dt class="section-number">Section <%= declarable.section_numeral %></dt>
        <dd class="section-title tariff-fragments"><%= link_to declarable.section, section_path(declarable.section), class: "js-pjax" %>
          <dl class="tariff-fragments">
            <dt class="chapter-code" title="Chapter code"><%= declarable.chapter_short_code %></dt>
            <dd><%= link_to declarable.chapter, chapter_path(declarable.chapter), class: "js-pjax" %>
              <dl>
                <dt class="heading-code" title="Heading code"><%= declarable.heading_display_short_code %></dt>
                <% if declarable.show_commodity_tree? %>
                  <dd><%= link_to declarable.heading.to_s.html_safe, heading_path(declarable.heading), class: "js-pjax" %>
                      <%= commodity_tree(declarable, declarable.ancestors) %>
                  </dd>
                <% else %>
                  <dd class="declarable">
                    <%= declarable_heading(declarable) %>
                  </dd>
                <% end %>
              </dl>
            </dd>
          </dl>
        </dd>
      </dl>
    </nav>
  </div>
  <%= render 'measures/measures', declarable: declarable %>
</article>

<% content_for :title, "#{declarable.description_plain} - Trade Tariff - GOV.UK" %>

<article class="tariff commodity">
  <div class="inner">
    <nav class="trail">
      <dl>
        <dt class="section-number">Section <%= declarable.section_numeral %></dt>
        <dd class="section-title tariff-fragments"><%= link_to declarable.section, section_path(declarable.section), class: "js-pjax" %>
          <dl class="tariff-fragments">
            <dt class="chapter-code" title="Chapter code"><%= declarable.chapter_short_code %></dt>
            <dd><%= link_to declarable.chapter, chapter_path(declarable.chapter), class: "js-pjax" %>
              <dl>
                <dt class="heading-code" title="Heading code"><%= declarable.heading_display_short_code %></dt>
                <% if declarable.show_commodity_tree? %>
                  <dd><%= link_to declarable.heading.to_s.html_safe, heading_path(declarable.heading), class: "js-pjax" %>
                      <%= commodity_tree(declarable, declarable.ancestors) %>
                  </dd>
                <% else %>
                  <dd class="declarable">
                    <%= declarable_heading(declarable) %>
                  </dd>
                <% end %>
              </dl>
            </dd>
          </dl>
        </dd>
      </dl>
    </nav>
  </div>
  <%= render 'measures/measures', declarable: declarable %>
</article>

Use dashes to separate heading words
Use dashes to separate heading words

Dashes are used everywhere else in this project and across GOV.UK this should follow that standard.