Merge pull request #14673 from twbs/restore_sr_friendly_collapse

More screenreader friendly Collapse, Take 2

less/component-animations.less

@@ -17,8 +17,9 @@
 
 .collapse {
   display: none;
+  visibility: hidden;
 
-  &.in      { display: block; }
+  &.in      { display: block; visibility: visible; }
   tr&.in    { display: table-row; }
   tbody&.in { display: table-row-group; }
 }
@@ -27,5 +28,7 @@
   position: relative;
   height: 0;
   overflow: hidden;
-  .transition(height .35s ease);
+  .transition-property(~"height, visibility");
+  .transition-duration(.35s);
+  .transition-timing-function(ease);
 }

less/navbar.less

@@ -67,6 +67,7 @@
 
     &.collapse {
       display: block !important;
+      visibility: visible !important;
       height: auto !important;
       padding-bottom: 0; // Override default setting
       overflow: visible !important;

less/navs.less

@@ -223,9 +223,11 @@
 .tab-content {
   > .tab-pane {
     display: none;
+    visibility: hidden;
   }
   > .active {
     display: block;
+    visibility: visible;
   }
 }