title: How to validate hook block configure form in Drupal 7
body: <p>In Drupal 7 <a href="http://api.drupal.org/api/drupal/modules!block!block.api.php/function/hook_block_configure/7" rel="nofollow">hook_block_configure</a> and <a href="http://api.drupal.org/api/drupal/modules!block!block.api.php/function/hook_block_save/7" rel="nofollow">hook_block_save</a> provide a method to modify a blocks settings and save these values. </p>
  
  <p>But how would I carry out validation on the form before saving the values?</p>