Merge pull request #14444 from twbs/sr_friendly_hidden_content

More screenreader friendly hidden content

dist/css/bootstrap.css

@@ -3178,9 +3178,11 @@ input[type="button"].btn-block {
 }
 .collapse {
   display: none;
+  visibility: hidden;
 }
 .collapse.in {
   display: block;
+  visibility: visible;
 }
 tr.collapse.in {
   display: table-row;
@@ -3846,9 +3848,11 @@ select[multiple].input-group-sm > .input-group-btn > .btn {
 }
 .tab-content > .tab-pane {
   display: none;
+  visibility: hidden;
 }
 .tab-content > .active {
   display: block;
+  visibility: visible;
 }
 .nav-tabs .dropdown-menu {
   margin-top: -1px;

docs/dist/css/bootstrap.css

@@ -3178,9 +3178,11 @@ input[type="button"].btn-block {
 }
 .collapse {
   display: none;
+  visibility: hidden;
 }
 .collapse.in {
   display: block;
+  visibility: visibile;
 }
 tr.collapse.in {
   display: table-row;
@@ -3846,9 +3848,11 @@ select[multiple].input-group-sm > .input-group-btn > .btn {
 }
 .tab-content > .tab-pane {
   display: none;
+  visibility: hidden;
 }
 .tab-content > .active {
   display: block;
+  visibility: visible;
 }
 .nav-tabs .dropdown-menu {
   margin-top: -1px;

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; }
 }

less/navs.less

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