Index: modules/system/system.css
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.css,v
retrieving revision 1.56
diff -u -p -r1.56 system.css
--- modules/system/system.css	31 Jul 2009 11:20:42 -0000	1.56
+++ modules/system/system.css	3 Aug 2009 09:39:57 -0000
@@ -564,3 +564,31 @@ div.password-suggestions ul {
 div.password-confirm {
   visibility: hidden;
 }
+
+/**
+ * Hide elements from all users.
+ *
+ * Used for elements that should not be immediately displayed to any user. An
+ * example may be a collapsable fieldset, that will be expanded by an action
+ * from a user. The effect of this class can be toggled with the JQuery show()
+ * and hide() functions.
+ */
+.element-hidden {
+  display: none;
+}
+
+/**
+ * Hide elements visually, but keep them available for screen-readers.
+ *
+ * Used for information required for screen-reader users to understand and use
+ * the site where visual display is undesirable. Information provided in this
+ * manner should be kept concise, to avoid unnecessary burden on the user.
+ */
+.element-invisible {
+  position: absolute;
+  left: -10000px;
+  top: auto;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+}
Index: modules/system/system-rtl.css
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system-rtl.css,v
retrieving revision 1.15
diff -u -p -r1.15 system-rtl.css
--- modules/system/system-rtl.css	20 Apr 2009 20:07:14 -0000	1.15
+++ modules/system/system-rtl.css	3 Aug 2009 09:39:57 -0000
@@ -115,3 +115,19 @@ div.indentation {
 div.tree-child, div.tree-child-last {
   background-position: -65px center;
 }
+
+/**
+ * Hide elements visually, but keep them available for screen-readers.
+ *
+ * Used for information required for screen-reader users to understand and use
+ * the site where visual display is undesirable. Information provided in this
+ * manner should be kept concise, to avoid unnecessary burden on the user.
+ */
+.element-invisible {
+  position: absolute;
+  left: 10000px;
+  top: auto;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+}