title: Add a rel nofollow to shortcode in wordpress
body: <p>I use a button shortcode for my WordPress (see below).</p>
  
  <p>As you can see, I can choose a color, put the link, specify something for the target attribute.</p>
  
  <p>I would like to add rel nofollow to this wordpress button link shortcode but I don't know how to do it.</p>
  
  <pre><code>add_shortcode('button', 'shortcode_button');
  function shortcode_button($atts, $content = null) {
      $atts = shortcode_atts(
          array(
              'color' =&gt; 'black',
              'link' =&gt; '#',
              'target' =&gt; '',
          ), $atts);
  
          return '[raw]&lt;span class="button ' . $atts['color'] . '"&gt;&lt;a href="' . $atts['link'] . '" target="' . $atts['target'] . '"&gt;' .do_shortcode($content). '&lt;/a&gt;&lt;/span&gt;[/raw]';
  }
  </code></pre>
  
  <p>Thanks</p>