Screen Reader Content
Careful consideration needs to be taken when deciding how content should be hidden. For example, sometimes content needs to be hidden from users, but visible to people using screen readers.
One common reason for doing this is if you were to use icons on your page without any supporting text. People without a screen reader could see the icons and understand the context of the icon, but people using a screen reader could not. By using the .screen-reader class, content is hidden from anybody viewing the website on a monitor, but can still read by a screen reader.
Using aria-hidden="true" for our icon font ensures that our icons are not read by a screen reader. I highly suggest reading the Filament Group's article to learn more about this fallback.