protected function buildLookupTable() {
    $this->lookupTable = [];
    foreach ($this->configArray as $section => $entry) {
      // create section entry
      $lookupSectionKey = strtolower($section.':');
      $this->lookupTable[$lookupSectionKey] = [$section];
      // create key entries
      foreach ($entry as $key => $value) {
        $lookupKey = strtolower($lookupSectionKey.$key);
        $this->lookupTable[$lookupKey] = [$section, $key];
      }
    }
  }