PHP post jQueryUI menu selection

I have a jQuery UI menu inside a form and I would like to be able to pass the tag attribute as value for my POST in PHP.

Does anybody know how I can do that? I only know how to get that value via JavaScript.

Example:

<form id="cities" name="cities">
   <ul id="menu" style="position:absolute;">
     <li><a href="#" tag="LDN">Lodon</a></li>
     <li><a href="#" tag="MAD">Madrid</a></li>
     <li><a href="#" tag="LYN">Lyon</a></li>
     <li><a href="#" tag="PAR">Paris</a></li>
   </ul>
   ... other input fields...  
   ... a submit button
</form>

I want to POST/GET the tag to the next PHP page.

<?php
   // How can I get the tag or just the menu selection value (Lyon, Paris, etc) 
      and save it to a variable in PHP?
   // I'm more interested in the tag
?>

Thanks in advance for your help,

Cristina

DEMO

JS code:

$(function() {
     $( "#menu" ).menu({
         select:function(event, ui){
             console.log(ui.item);
             alert("Selected tag = "+$(ui.item).find('a').attr('tag'));
             $('#tag').val($(ui.item).find('a').attr('tag'));
         }
     });
});

HTML:

<form id="cities" name="cities">
   <ul id="menu" >
     <li><a href="#" tag="LDN">Lodon</a></li>
     <li><a href="#" tag="MAD">Madrid</a></li>
     <li><a href="#" tag="LYN">Lyon</a></li>
     <li><a href="#" tag="PAR">Paris</a></li>
   </ul>
    <br style="clear:both;">
    Selected menu tag (hidden field):
        <input type="text" id="tag" name="tag">

</form>