--- shurly.old.module	2010-08-30 14:12:12.000000000 +0100
+++ shurly.module	2010-12-03 16:14:34.000000000 +0000
@@ -438,8 +438,13 @@ function shurly_shorten($long_url, $cust
   if (!$rate_limit['allowed']) {
     $error = t('Rate limit exceeded. You are limited to @rate requests per @time minute period.', array('@rate' => $rate_limit['rate'], '@time' => $rate_limit['time']));
   }
-  elseif (!shurly_validate_long($long_url)) {
-    $error = t('Invalid long URL.');
+  elseif ($errors = module_invoke_all('shurly_validate', $long_url)) { 
+    // Creates hook_shurly_validate($long_url).
+    // Implementations of this hook should return error strings through t().
+    // See, for example, shurly_shurly_validate($long_url) below.
+    if (count($errors)) {
+      $error = implode(' ', $errors);
+    }
   }
   elseif (is_null($custom)) {
     $latest = shurly_get_latest_short($long_url, $account->uid);
@@ -604,6 +609,16 @@ function shurly_validate_custom($custom)
   return preg_match('/[\/#%&\@\*\{\}\\:\;<>\?\+ \.\,\'\"\$\|`^\[\]]/u', $custom) ? FALSE : TRUE;
 }
 
+/**
+ * Implementation of hook_shurly_validate().
+ */
+function shurly_shurly_validate($long_url) {
+  if (!shurly_validate_long(&$long_url)) {
+    return t('Invalid long URL.');
+  }
+  return;
+}
+
 
 function shurly_validate_long(&$long_url) {
   $return = TRUE;