code: protected function getMeta($level, &$context)
      {
          $haveException = isset($context['exception']) &&
              ($context['exception'] instanceof \Exception
                  || PHP_VERSION_ID >= 70000 && $context['exception'] instanceof \Throwable);
          $isError = \in_array($level, array('emergency','critical','error','warning','notice'));
          $metaVals = \array_intersect_key($context, \array_flip(array('file','line')));
          $metaVals['psr3level'] = $level;
          $context = \array_diff_key($context, $metaVals);
          if ($haveException) {
              $exception = $context['exception'];
              $metaVals = \array_merge(array(
                  'backtrace' => $this->debug->errorHandler->backtrace($exception),
                  'file' => $exception->getFile(),
                  'line' => $exception->getLine(),
              ), $metaVals);
          } elseif ($isError && \count($metaVals) < 2) {
              $callerInfo = $this->debug->utilities->getCallerInfo(1);
              $metaVals = \array_merge(array(
                  'file' => $callerInfo['file'],
                  'line' => $callerInfo['line'],
              ), $metaVals);
          }
          if (!$context) {
              $context = $this->debug->meta();
          }
          return $this->debug->meta($metaVals);
      }
docs: Exctract potential meta values from $context
  
  @param string $level   log level
  @param array  $context context array
  meta values get removed
  
  @return array meta