title: Saving all values in "multiple select"
body: <p>im having a metabox in wordpress with a mutliple select form. </p>
  
  <pre><code>&lt;select name="my_meta_box_select" id="my_meta_box_select" multiple="" style="width:300px; height:400px;"&gt;
      &lt;option value="red"&gt;Red
      &lt;/option&gt;
      &lt;option value="blue"&gt;Blue
      &lt;/option&gt;
  &lt;/select&gt;
  </code></pre>
  
  <p>So far so good, the selected value gets saved and I am able to retrieve it, however I wish for both values to be saved.</p>
  
  <p>For example I wish to save both red AND blue and be able to retrieve it from the frontend. Is there any way to achieve this? Are there better forms than a select?</p>
  
  <p>The purpose is for a user to select pages from one select field to another and then save the second select field.</p>
  
  <p>select 1: </p>
  
  <p>red</p>
  
  <p>blue</p>
  
  <p>green</p>
  
  <p>Select 2:</p>
  
  <p>orange</p>
  
  <p>-button-</p>
  
  <p>Now if a user where to select <code>red</code> and <code>blue</code> from <code>select 1</code> and then press <code>-button-</code> the values will be added to select 2. When I now press update page I wish to save all the values in select 2.</p>
  
  <p>This is how i save from my current select field (but it only saves ONE selected value)</p>
  
  <pre><code>if( isset( $_POST['my_meta_box_select'] ) )
      update_post_meta( $post_id, 'my_meta_box_select', esc_attr( $_POST['my_meta_box_select'] ) );
  </code></pre>