_mixins.scss in font-awesome-sass-4.6.1

- old
+ new
@@ -6,20 +6,55 @@
   font: normal normal normal #{$fa-font-size-base}/#{$fa-line-height-base} FontAwesome; // shortening font declaration
   font-size: inherit; // can't have font-size inherit on line above, so need to override
   text-rendering: auto; // optimizelegibility throws things off #1094
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
+
 }
 
 @mixin fa-icon-rotate($degrees, $rotation) {
-  filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation});
+  -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation})";
   -webkit-transform: rotate($degrees);
       -ms-transform: rotate($degrees);
           transform: rotate($degrees);
 }
 
 @mixin fa-icon-flip($horiz, $vert, $rotation) {
-  filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation});
+  -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(rotation=#{$rotation}, mirror=1)";
   -webkit-transform: scale($horiz, $vert);
       -ms-transform: scale($horiz, $vert);
           transform: scale($horiz, $vert);
+}
+
+
+// Only display content to screen readers. A la Bootstrap 4.
+//
+// See: http://a11yproject.com/posts/how-to-hide-content/
+
+@mixin sr-only {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  padding: 0;
+  margin: -1px;
+  overflow: hidden;
+  clip: rect(0,0,0,0);
+  border: 0;
+}
+
+// Use in conjunction with .sr-only to only display content when it's focused.
+//
+// Useful for "Skip to main content" links; see http://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G1
+//
+// Credit: HTML5 Boilerplate
+
+@mixin sr-only-focusable {
+  &:active,
+  &:focus {
+    position: static;
+    width: auto;
+    height: auto;
+    margin: 0;
+    overflow: visible;
+    clip: auto;
+  }
 }