What are selectors?

            

              <div id="body">
              
<h2>Some Header</h2>
              

                <div class="contents">
                  
<p>Paragraph 1</p>
                  
<p>Paragraph 2</p>
                </div>
              

                <div class="contents2">
                  
<p>Paragraph 1<p>
                  
<p>Paragraph 2<p>
                </div>
              

                <div class="contents">
                  <span>Span tag</span>
                </div>
              
              </div>