code: private function resolveSubset($setName, $setValue)
      {
          $rules = $this->getSetDefinition($setName);
          foreach ($rules as $name => $value) {
              if ('@' === $name[0]) {
                  $set = $this->resolveSubset($name, $setValue);
                  unset($rules[$name]);
                  $rules = array_merge($rules, $set);
              } elseif (!$setValue) {
                  $rules[$name] = false;
              } else {
                  $rules[$name] = $value;
              }
          }
  
          return $rules;
      }
docs: Resolve set rules as part of another set.
  
  If set value is false then disable all fixers in set,
  if not then get value from set item.
  
  @param string $setName
  @param bool   $setValue
  
  @return array