title: Alt text for Unicode/Emojis in HTML/CSS without JavaScript?
body: <p>I want to detect a situation when browser displays a placeholder (▯, �, etc)  instead of  a Unicode character, say ⏻. Either browser does not support font fallback, or a font that supports a character is not installed. I would like to replace the unsupported character with alt text, similar to <code>&lt;img&gt;</code> tag. For ⏻ it would be something like "Turn on/off" or "Power button".</p>
  
  <p>Is there a way to do so in HTML and CSS without JavaScript?</p>