What HTML5 tag should be used for filtering search results.

HTML5 provides semantic elements for organizing content, but there's no specific tag exclusively for filtering search results. The best approach is to use a combination of semantic elements with appropriate roles and structure.

Recommended Structure for Search Filters

Use the <aside> element with filter controls inside a <form> for better semantics and accessibility:

<section id="search-results">
   <h1>Search Results</h1>
   
   <aside class="search-filters" role="complementary">
      <h2>Filter Results</h2>
      <form>
         <fieldset>
            <legend>Category</legend>
            <input type="checkbox" id="books" value="books">
            <label for="books">Books</label>
            <input type="checkbox" id="electronics" value="electronics">
            <label for="electronics">Electronics</label>
         </fieldset>
         
         <fieldset>
            <legend>Price Range</legend>
            <input type="range" id="price" min="0" max="1000">
            <label for="price">Max Price: $1000</label>
         </fieldset>
      </form>
   </aside>

   <main class="results-container">
      <article>
         <h3>Search Result 1</h3>
         <p>Description of result...</p>
      </article>
      
      <article>
         <h3>Search Result 2</h3>
         <p>Description of result...</p>
      </article>
   </main>
</section>

Alternative: Using nav Element

For filter navigation, you can also use the <nav> element:

<section id="search-results">
   <h1>Search Results</h1>
   
   <nav class="filter-nav" aria-label="Search filters">
      <ul>
         <li><a href="?category=books">Books</a></li>
         <li><a href="?category=electronics">Electronics</a></li>
         <li><a href="?price=low">Price: Low to High</a></li>
      </ul>
   </nav>

   <div class="results-container">
      <!-- search results -->
   </div>
</section>

Why Not Use header?

The <header> element is intended for introductory content or navigation aids for its section. While technically valid, it's less semantic than <aside> or <nav> for filters.

Best Practices

Conclusion

Use <aside> with <form> elements for interactive filters, or <nav> for filter links. Both provide better semantics and accessibility than <header> for search result filtering.