code: private function clearLog($flags)
      {
          $return = null;
          $clearErrors = $flags & Debug::CLEAR_LOG_ERRORS;
          if ($flags & Debug::CLEAR_LOG) {
              $return = 'log ('.($clearErrors ? 'incl errors' : 'sans errors').')';
              $curDepth = 0;
              foreach ($this->data['groupStacks']['main'] as $group) {
                  $curDepth += (int) $group['collect'];
              }
              $entriesKeep = $this->debug->internal->getCurrentGroups($this->data['log'], $curDepth);
              $this->clearLogHelper($this->data['log'], $clearErrors, $entriesKeep);
          } elseif ($clearErrors) {
              $return = 'errors';
          }
          return $return;
      }
docs: Clear log entries
  
  @param integer $flags flags passed to clear()
  
  @return string|null