The objective of this technique is to show how to provide a semantically identified icon font that does not disappear if a user overrides font-family via user stylesheet, script, or extension. The point is to provide a technique to differentiate icons fonts from general font (text) usage.
Some low vision users rely on user stylesheets to override fonts to perceive content. However, they need to be able to perceive icon fonts that are meaningful, for instance indicators (e.g. a star signifying a favorite) and interactive ones (e.g. an email link).
The key is for the author to semantically markup icon fonts with role="img". Then the user's font replacement selector can hook into that semantic and exclude role="img". This results in those icon fonts being shown.