code: function(sortString, command) {
              var self        = this,
                  rules       = sortString.split(' '),
                  current     = command,
                  rule        = [],
                  i           = -1;
  
              // command.sortString = sortString;
  
              for (i = 0; i < rules.length; i++) {
                  rule = rules[i].split(':');
  
                  current.sortString  = rules[i];
                  current.attribute   = h.dashCase(rule[0]);
                  current.order       = rule[1] || 'asc';
  
                  switch (current.attribute) {
                      case 'default':
                          // treat "default" as sorting by no attribute
  
                          current.attribute = '';
  
                          break;
                      case 'random':
                          // treat "random" as an order not an attribute
  
                          current.attribute   = '';
                          current.order       = 'random';
  
                          break;
                  }
  
                  if (!current.attribute || current.order === 'random') break;
  
                  if (i < rules.length - 1) {
                      // Embed reference to the next command
  
                      current.next = new mixitup.CommandSort();
  
                      h.freeze(current);
  
                      current = current.next;
                  }
              }
  
              return self.callFilters('commandsParseSort', command, arguments);
          }
docs: Parses user-defined sort strings (i.e. `default:asc`) into sort commands objects.
  
  @private
  @instance
  @since   3.0.0
  @param   {string}                sortString
  @param   {mixitup.CommandSort}   command
  @return  {mixitup.CommandSort}