* **This class (.text-sr) should not be used on HTML elements**. It is meant to only be used as a Sass extend (originally using the class-based extend method). its been upgraded to use the new Sass placeholder extend method (%text-sr) and won't work if directly applied to HTML. If you're looking for a canned class that will apply the %text-sr exend, you can use .sr without any problems or worries of it becoming obsolete. If this is an element that's known to be consistently hidden visually in a layout, your other option is to define that hidden trait within our Sass Archtiecture (assuming there's a clear logical place for the selector/rule to be added). The syntax for that is just #mathjax-accessibility-message { @extend %text-sr}.
* Also, I'd consider adding a few classes (message message-accessibility) to this containing div for more general UI/visual control. 
* Double also, the contents of the message should be wrapped in semantic elements as well - in this case &lt;p&gt; elements are appropriate. If you want to add a title, any semantic heading tag will do too (we add a class of .title to any semantic title in a message, FYI).