diff --git a/includes/ajax.inc b/includes/ajax.inc
index 8905687..bff41c1 100644
--- a/includes/ajax.inc
+++ b/includes/ajax.inc
@@ -143,6 +143,19 @@
  * - #ajax['event']: The JavaScript event to respond to. This is normally
  *   selected automatically for the type of form widget being used, and
  *   is only needed if you need to override the default behavior.
+ * - #ajax['prevent']: A JavaScript event to prevent when 'event' is triggered.
+ *   When binding #ajax behaviors to form buttons, pressing the ENTER key within
+ *   a textfield triggers the click event of the form's first submit button.
+ *   Triggering Ajax in this situation leads to problems, like breaking
+ *   autocomplete textfields. Because of that, #ajax behaviors are bound to the
+ *   mousedown event on form buttons by default. However, binding to mousedown
+ *   rather than click means that it is possible to trigger a click by pressing
+ *   the mouse, holding the mouse button down until the Ajax request is complete
+ *   and the button is re-enabled, and then releasing the mouse button. For this
+ *   case, 'prevent' can be set to 'click', so an additional handler is bound to
+ *   prevent such a click from triggering a non-Ajax form submission. This also
+ *   prevents a textfield's ENTER press triggering a button's non-Ajax form
+ *   submission behavior.
  * - #ajax['method']: The jQuery method to use to place the new HTML.
  *   Defaults to 'replaceWith'. May be: 'replaceWith', 'append', 'prepend',
  *   'before', 'after', or 'html'. See the
@@ -591,6 +604,7 @@ function ajax_process_form($element, &$form_state) {
  *   An associative array containing the properties of the element.
  *   Properties used:
  *   - #ajax['event']
+ *   - #ajax['prevent']
  *   - #ajax['path']
  *   - #ajax['options']
  *   - #ajax['wrapper']