=== modified file 'includes/form.inc'
--- includes/form.inc	2009-12-17 21:59:31 +0000
+++ includes/form.inc	2009-12-28 17:18:55 +0000
@@ -2,6 +2,12 @@
 // $Id: form.inc,v 1.421 2009/12/17 21:59:31 dries Exp $
 
 /**
+ * Validate the section that is 1 level up from the button.
+ * @see _form_validate_allow()
+ */
+define('VALIDATE_SECTION_PARENT', -1);
+
+/**
  * @defgroup forms Form builder functions
  * @{
  * Functions that build an abstract representation of a HTML form.
@@ -884,7 +890,7 @@ function _form_validate(&$elements, &$fo
 
   // Recurse through all children.
   foreach (element_children($elements) as $key) {
-    if (isset($elements[$key]) && $elements[$key]) {
+    if (_form_validate_allowed($elements[$key], $form_state)) {
       _form_validate($elements[$key], $form_state);
     }
   }
@@ -947,6 +953,27 @@ function _form_validate(&$elements, &$fo
 }
 
 /**
+ * Check whether an element can be validated.
+ *
+ * If the clicked button specifies sections to be validated then #array_parents
+ * is checked to be starting with one of sections.
+ */
+function _form_validate_allowed($elements, $form_state) {
+  if (empty($form_state['clicked_button']['#validate_sections'])) {
+    return TRUE;
+  }
+  foreach ($form_state['clicked_button']['#validate_sections'] as $section) {
+    if (is_int($section) && $section < 0) {
+      $section = array_slice($form_state['clicked_button']['#array_parents'], 0, $section);
+    }
+    if (count($element['#array_parents']) >= count($section) && array_slice($element['#array_parents'], 0, count($section)) === $section) {
+      return TRUE;
+    }
+  }
+  return FALSE;
+}
+
+/**
  * A helper function used to execute custom validation and submission
  * handlers for a given form. Button-specific handlers are checked
  * first. If none exist, the function falls back to form-level handlers.
@@ -967,8 +994,9 @@ function form_execute_handlers($type, &$
   if (isset($form_state[$type . '_handlers'])) {
     $handlers = $form_state[$type . '_handlers'];
   }
-  // Otherwise, check for a form-level handler.
-  elseif (isset($form['#' . $type])) {
+  // Otherwise, check for a form-level handler. If a per-button validate is in
+  // effect then neither the validate nor the submit handler should fire.
+  elseif (isset($form['#' . $type]) && empty($form_state['clicked_button']['#validate_sections'])) {
     $handlers = $form['#' . $type];
   }
   else {
@@ -1006,7 +1034,7 @@ function form_execute_handlers($type, &$
  * @param $message
  *   The error message to present to the user.
  * @return
- *   Return value is for internal use only. To get a list of errors, use 
+ *   Return value is for internal use only. To get a list of errors, use
  *   form_get_errors() or form_get_error().
  */
 function form_set_error($name = NULL, $message = '') {
@@ -3261,7 +3289,7 @@ function batch_process($redirect = NULL,
   $batch =& batch_get();
 
   drupal_theme_initialize();
-  
+
   if (isset($batch)) {
     // Add process information
     $process_info = array(
@@ -3276,7 +3304,7 @@ function batch_process($redirect = NULL,
     );
     $batch += $process_info;
 
-    // The batch is now completely built. Allow other modules to make changes to the 
+    // The batch is now completely built. Allow other modules to make changes to the
     // batch so that it is easier to reuse batch processes in other enviroments.
     drupal_alter('batch', $batch);
 

=== modified file 'modules/field/field.form.inc'
--- modules/field/field.form.inc	2009-12-21 13:47:31 +0000
+++ modules/field/field.form.inc	2009-12-28 16:48:58 +0000
@@ -214,6 +214,7 @@ function field_multiple_value_form($fiel
           '#name' => $field_name . '_add_more',
           '#value' => t('Add another item'),
           '#attributes' => array('class' => array('field-add-more-submit')),
+          '#validate_sections' => array(VALIDATE_SECTION_PARENT),
           // Submit callback for disabled JavaScript.
           '#submit' => array('field_add_more_submit'),
           '#ajax' => array(

=== modified file 'modules/poll/poll.module'
--- modules/poll/poll.module	2009-12-14 20:38:15 +0000
+++ modules/poll/poll.module	2009-12-28 15:54:16 +0000
@@ -273,6 +273,7 @@ function poll_form($node, &$form_state) 
     '#value' => t('More choices'),
     '#description' => t("If the amount of boxes above isn't enough, click here to add more choices."),
     '#weight' => 1,
+    '#validate_sections' => array(VALIDATE_SECTION_PARENT),
     '#submit' => array('poll_more_choices_submit'), // If no javascript action.
     '#ajax' => array(
       'callback' => 'poll_choice_js',
@@ -901,4 +902,3 @@ function poll_user_cancel($edit, $accoun
       break;
   }
 }
-

=== modified file 'modules/simpletest/tests/form.test'
--- modules/simpletest/tests/form.test	2009-12-17 17:18:02 +0000
+++ modules/simpletest/tests/form.test	2009-12-28 16:53:11 +0000
@@ -231,6 +231,21 @@ class FormValidationTestCase extends Dru
     $this->assertNoFieldByName('name', t('Form element was hidden.'));
     $this->assertText('Name value: element_validate_access', t('Value for inaccessible form element exists.'));
   }
+
+  /**
+   * Test button press validates a section.
+   */
+  function testValidateParents() {
+    $edit = array('test' => 'pass');
+    foreach(array('form-test/validate-sections', 'form-test/validate-sections-parent') as $path) {
+      $this->drupalPost($path, $edit, t('Partial validate'));
+      $this->assertNoText(t('!name field is required.', array('!name' => 'Title')));
+      $this->assertText('Test is validated');
+      $this->drupalPost($path, $edit, t('Full validate'));
+      $this->assertText(t('!name field is required.', array('!name' => 'Title')));
+      $this->assertText('Test is validated');
+    }
+  }
 }
 
 /**

=== modified file 'modules/simpletest/tests/form_test.module'
--- modules/simpletest/tests/form_test.module	2009-12-17 17:18:02 +0000
+++ modules/simpletest/tests/form_test.module	2009-12-28 16:57:22 +0000
@@ -17,6 +17,20 @@ function form_test_menu() {
     'access arguments' => array('access content'),
     'type' => MENU_CALLBACK,
   );
+  $items['form-test/validate-sections'] = array(
+    'title' => 'Form validation sections test',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('form_test_validate_sections'),
+    'access arguments' => array('access content'),
+    'type' => MENU_CALLBACK,
+  );
+  $items['form-test/validate-sections-parent'] = array(
+    'title' => 'Form validation sections test',
+    'page callback' => 'drupal_get_form',
+    'page arguments' => array('form_test_validate_sections_parent'),
+    'access arguments' => array('access content'),
+    'type' => MENU_CALLBACK,
+  );
 
   $items['form_test/tableselect/multiple-true'] = array(
     'title' => 'Tableselect checkboxes test',
@@ -203,6 +217,62 @@ function form_test_validate_form_validat
   }
 }
 
+function form_test_validate_sections($form) {
+  $form['title'] = array(
+    '#type' => 'textfield',
+    '#title' => 'Title',
+    '#required' => TRUE,
+  );
+  $form['wrapper']['test'] = array(
+    '#type' => 'textfield',
+    '#element_validate' => array('form_test_validate_test_element'),
+  );
+  $form['buttons']['partial'] = array(
+    '#type' => 'submit',
+    '#validate_sections' => array(array('wrapper')),
+    '#value' => t('Partial validate'),
+  );
+  $form['buttons']['full'] = array(
+    '#type' => 'submit',
+    '#value' => t('Full validate'),
+  );
+  return $form;
+}
+
+/**
+ * Element handler for the test element.
+ */
+function form_test_validate_test_element($form, $form_state) {
+  if ($form_state['values']['test'] == 'pass') {
+    drupal_set_message('Test is validated');
+  }
+}
+
+/**
+ * Tests the VALIDATE_SECTION_PARENT constant.
+ */
+function form_test_validate_sections_parent($form) {
+  $form['title'] = array(
+    '#type' => 'textfield',
+    '#title' => 'Title',
+    '#required' => TRUE,
+  );
+  $form['wrapper']['test'] = array(
+    '#type' => 'textfield',
+    '#element_validate' => array('form_test_validate_test_element'),
+  );
+  $form['wrapper']['partial'] = array(
+    '#type' => 'submit',
+    '#validate_sections' => array(VALIDATE_SECTION_PARENT),
+    '#value' => t('Partial validate'),
+  );
+  $form['buttons']['full'] = array(
+    '#type' => 'submit',
+    '#value' => t('Full validate'),
+  );
+  return $form;
+}
+
 /**
  * Create a header and options array. Helper function for callbacks.
  */
@@ -895,7 +965,7 @@ function form_test_state_persist($form, 
 
 /**
  * Submit handler.
- * 
+ *
  * @see form_test_state_persist()
  */
 function form_test_state_persist_submit($form, &$form_state) {
@@ -905,7 +975,7 @@ function form_test_state_persist_submit(
 
 /**
  * Implements hook_form_FORM_ID_alter().
- * 
+ *
  * @see form_test_state_persist()
  */
 function form_test_form_form_test_state_persist_alter(&$form, &$form_state) {