apt-get 配置文件中使用什么语言？

Question

例如，/etc/apt/apt.conf.d/50unattended-upgrades我们有这样的内容：

// Automatically upgrade packages from these (origin:archive) pairs
Unattended-Upgrade::Allowed-Origins {
    "${distro_id}:${distro_codename}-security";
//  "${distro_id}:${distro_codename}-updates";
//  "${distro_id}:${distro_codename}-proposed";
//  "${distro_id}:${distro_codename}-backports";
};

// List of packages to not update (regexp are supported)
Unattended-Upgrade::Package-Blacklist {
//  "vim";
//  "libc6";
//  "libc6-dev";
//  "libc6-i686";
};

这里使用什么语言？