protected function getPreparedCssContent()
    {
        if ($this->preparedContent === null) {
            $this->preparedContent = Placeholder::replaceStringsAndComments($this->getCssContent());

            // Move comments from the end of the line to the beginning to make it easier to
            // detect, to which rule they belong to
            $this->preparedContent = preg_replace(
                '/^([^\r\n]+)(_COMMENT_[a-f0-9]{32}_)([\r\n\t\f]+)/m',
                "\\2\n\\1\\3",
                $this->preparedContent
            );

            // Remove white space characters before comments
            $this->preparedContent = preg_replace(
                '/^([ \t\f]*)(_COMMENT_[a-f0-9]{32}_)/m',
                "\\2\n",
                $this->preparedContent
            );

            // Very important: Split long lines, because parsing long lines (char by char) costs a lot performance
            // (several thousand percent...).
            $this->preparedContent = str_replace(["{", "}", ";"], ["{\n", "}\n", ";\n"], $this->preparedContent);
        }

        return $this->preparedContent;
    }