{live} makes part of a page interactive without JavaScript of your own. A click on an element with pad-click inside the region posts the event to the page; the page runs again on the server, and only the region comes back and is swapped in.

<?php

  $count = (int) padLiveValue ();

  if ( padLiveEvent () == 'add'   ) $count++;
  if ( padLiveEvent () == 'reset' ) $count = 0;

?>

{live 'counter'}
  <p>Clicked {$count} times</p>
  <button pad-click="add" pad-value="{$count}">Add one</button>
  <button pad-click="reset">Reset</button>
{/live}

• pad-click="add" on any element, pad-submit="save" on a form (its fields come along as ordinary request values), pad-change="pick" on a field (its name and value come along); pad-value adds a value to the event.
• The page's PHP reads the event with padLiveEvent() and its value with padLiveValue(); both are empty on an ordinary request.
• State lives where a page keeps it: in the value the event carries, as here, in the session ($padSessionVars), or in a database.
• The region is a <div data-pad-live="name">; the first region of a page brings the small script that does the posting and swapping.