protected function openTrace()
    {
        $index = \count($this->traces);

        $this->traces[$index] = [];
        $this->trace =& $this->traces[$index];

        $this->indents[$index] = [];
        $this->indent =& $this->indents[$index];

        if ($this->performStatistics) {
            $this->statistics[$index] = [];
            $this->statistic =& $this->statistics[$index];
        }
    }