Have seen a code in a CSS content property that I can't understand where it is defined

I'm looking at some code which has the following content property value for a pseudeo element - "\e90c". I understand this is some sort of escape code which represents a character or icon but where can I find what this icon would be? I haven't found an example of it online. I did find some links which showed me a paint-format icon but it's not that.

I don't know css codes very well so I'm not sure how it works or where it would be coming from.

Updated - The font-family being used is icomoon, but I couldn't understand how it's working after reading through their site.

Solution

It is deppending on the font used.

example: in the case of case of Mozilla Foundation Icon Font => simply test it :

p:after {
  font-family : 'foundation-icons';
  font-size   : 4em;
  content     : "\e90c"; 
  }

<link href="http://mozilla.github.io/foundation-icons/assets/foundation-icons.css" type="text/css" rel="stylesheet">

<p> and your icone is (in foundation-icons font ): </p>