title: In PHP, what is just a backtick (’)?
body: <p>I found this guide here, showing how to <a href="https://www.smashingmagazine.com/2011/10/create-custom-post-meta-boxes-wordpress/" rel="nofollow noreferrer">add a meta box in WordPress</a>.</p>
  <p>In there I can see this code:</p>
  <pre><code>/* Save the meta box’s post metadata. */
  function smashing_save_post_class_meta( $post_id, $post ) {
  
    /* Verify the nonce before proceeding. */
    if ( !isset( $_POST['smashing_post_class_nonce'] ) || !wp_verify_nonce( $_POST['smashing_post_class_nonce'], basename( __FILE__ ) ) )
      return $post_id;
  
    /* Get the post type object. */
    $post_type = get_post_type_object( $post-&gt;post_type );
  
    /* Check if the current user has permission to edit the post. */
    if ( !current_user_can( $post_type-&gt;cap-&gt;edit_post, $post_id ) )
      return $post_id;
  
    /* Get the posted data and sanitize it for use as an HTML class. */
    $new_meta_value = ( isset( $_POST['smashing-post-class'] ) ? sanitize_html_class( $_POST['smashing-post-class'] ) : ’ );
  
    /* Get the meta key. */
    $meta_key = 'smashing_post_class';
  
    /* Get the meta value of the custom field key. */
    $meta_value = get_post_meta( $post_id, $meta_key, true );
  
    /* If a new meta value was added and there was no previous value, add it. */
    if ( $new_meta_value &amp;&amp; ’ == $meta_value )
      add_post_meta( $post_id, $meta_key, $new_meta_value, true );
  
    /* If the new meta value does not match the old value, update it. */
    elseif ( $new_meta_value &amp;&amp; $new_meta_value != $meta_value )
      update_post_meta( $post_id, $meta_key, $new_meta_value );
  
    /* If there is no new meta value but an old value exists, delete it. */
    elseif ( ’ == $new_meta_value &amp;&amp; $meta_value )
      delete_post_meta( $post_id, $meta_key, $meta_value );
  }
  </code></pre>
  <p>What I don't get is the line using the tick <code>’</code>?
  Is that some kind of new notation or something smart?</p>
  <p>It's setting <code>$new_meta_value</code> to have the value <code>’</code> - and then later on checks if the value is equal to it. I mean... Why not using <code>null</code> or <code>false</code> or something?</p>
  <p>Usually I'd just frown and move on. But this code seems pretty carefully crafted.</p>