cpvalidator.module

<?php

   /**
    * Implementation of hook_webform_validation_validators().
    */
    function cpvalidator_webform_validation_validators() {
        return
            array(
                'validate_spanish_cp' => array(
                    'name' => 'Validates a spanish postal code',
                    'description' => t( 'Verifies the existence of this spanish postal code.' ),
                    'component_types' => array( 'textfield' ) )
             );
    }

   /**
    * Implementation of hook_webform_validation_validate().
    */
    function cpvalidator_webform_validation_validate($validator_name, $items, $components, $rule ) {

        // List of CP
        require_once("postalcodes.php");

        // Errors
        $error = 'El código postal tiene algún error, por favor revísalo';
        $numeric_error = 'El código postal debe ser un valor numérico';

        $errors = array();

         if ( $items ) {
            switch ( $validator_name ) {
                case 'validate_spanish_cp':

      				    foreach ($items as $key => $value) {

                      if(!preg_match('/[0-9]+/', $value)){
                          $errors[$key] = t( $numeric_error,
                            array( '%item' => $components[ $key ][ "name" ] ) );
                      }
                      else if( !in_array($value, $postal_codes) ) {
                          $errors[$key] = t( $error,
                            array( '%item' => $components[ $key ][ "name" ] ) );
                      }
                      return $errors;

                  }
                break;
            }
        }
    }

?>