diff --git a/includes/form.inc b/includes/form.inc
index a337b03..de1845c 100644
--- a/includes/form.inc
+++ b/includes/form.inc
@@ -130,6 +130,8 @@
  *   which may or may not be a button (in the case of Ajax forms.) This is
  *   often used to distinguish between various buttons in a submit handler,
  *   and is also used in Ajax handlers.
+ *   Note that the value of the triggering element is browser specific.
+ *   see http://dev.w3.org/html5/spec/association-of-controls-and-forms.html#implicit-submission
  * - 'cache': The typical form workflow involves two page requests. During the
  *   first page request, a form is built and returned for the user to fill in.
  *   Then the user fills the form in and submits it, triggering a second page