code: function symbolize (combo) {
          var map = {
            command   : '\u2318',     // ⌘
            shift     : '\u21E7',     // ⇧
            left      : '\u2190',     // ←
            right     : '\u2192',     // →
            up        : '\u2191',     // ↑
            down      : '\u2193',     // ↓
            'return'  : '\u23CE',     // ⏎
            backspace : '\u232B'      // ⌫
          };
          combo = combo.split('+');
  
          for (var i = 0; i < combo.length; i++) {
            // try to resolve command / ctrl based on OS:
            if (combo[i] === 'mod') {
              if ($window.navigator && $window.navigator.platform.indexOf('Mac') >=0 ) {
                combo[i] = 'command';
              } else {
                combo[i] = 'ctrl';
              }
            }
  
            combo[i] = map[combo[i]] || combo[i];
          }
  
          return combo.join(' + ');
        }
docs: Convert strings like cmd into symbols like ⌘
  @param  {String} combo Key combination, e.g. 'mod+f'
  @return {String}       The key combination with symbols