TIL Apt Takes 'Direct' In Proxy Statement

I was playing around in a contained network where only some of the connections should go through a proxy.

From man apt-transport-http:

The various APT configuration options support the special value DIRECT meaning that no proxy should be used. The environment variable no_proxy is also supported for the same purpose.

In my case:

# /etc/apt/apt.conf.d/99proxy

Acquire::http {
	Proxy "";
	Proxy::mirrors.tuna.tsinghua.edu.cn "DIRECT";
Acquire::https::Proxy "";