The old -getmode flag had two settings:
-getmode=local meant don't download from the network.
-getmode=vendor meant only use the vendor directory.
The new -mod flag has two settings:
-mod=readonly means refuse to automatically update go.mod (mainly for CI testing).
-mod=vendor means only use the vendor directory.
The old GOPROXY variable had two settings:
a proxy URL or else the empty string (direct connect).
The new GOPROXY variable has three settings:
a proxy URL, the string "off" (no network use allowed),
or else the empty string or the explicit string "direct" (direct connection).
We anticipate allow a comma-separated sequence in a future release,
so commas are disallowed entirely right now.