anchor.diff:          <% if @navigate_by_cluster %>
             <div class="block cluster">
               <h3><%= @site.word_for_clusters %></h3>
  -            <select name="clusters_ids" multiple>
  -              <option default>All clusters</option>
  +            <select name="clusters_ids" multiple placeholder="All clusters">
                 <% @clusters.each do |cluster| %>
                   <option value="<%= cluster.id %>"><%= cluster.title %></option>
                 <% end %>
  
positive.code: 
          <div class="block region">
            <h3><%= @site.word_for_regions %></h3>
            <select name="regions_ids" multiple>
              <option default>All regions</option>
              <% @regions.each do |region| %>
                <option value="<%= region.id %>"><%= region.title %>, <%= region.subtitle %></option>
              <% end %>
  
negative.code:         <% else %>
            <div class="block sectors">
              <h3><%= @site.word_for_clusters %></h3>
              <select name="sectors_ids" multiple placeholder="All sectors">
                <% @sectors.each do |sector| %>
                  <option value="<%= sector.id %>"><%= sector.title %></option>
                <% end %>
  