<button class="btn" type="submit"><p class="icon-search"></p>

Question

Element p not allowed as child of element button in this context. (Suppressing further errors from this subtree.)

<form action="{% url search %}" class="">
        <div class="input-append">
            <input size="16"
                   placeholder='{% trans "Search" %}'
                   type="text"
                   name="q"
                   value="{{ request.REQUEST.q }}">
            <button class="btn" type="submit"><p class="icon-search"></p>
            </button>
        </div>
    </form>

Answer 1

According to the W3C specification, the <button> element can only contain content such as text or images - specifically, "phrasing elements" (you can find a full list here). The <p> element is not included in this list of elements, so the HTML you give will fail validation against the specification.

Hope this helps!

On a different note, please try to improve the quality of your questions, as your current one is fairly unclear, making it difficult to help you.