`ENV` syntax `ENV <key>=<value>` barely documented

[adelton]

The https://github.com/containers/common/blob/main/docs/Containerfile.5.md says

ENV -- ENV <key> <value> The ENV instruction sets the environment variable to the value <value>.

So it only shows the syntax of key and value separated by space.

But the next paragraph says

Note that setting "ENV DEBIAN_FRONTEND=noninteractive" may ...

so it suddenly suggests that the format with the = sign also works.

I've now tested with podman-5.3.0-1.fc41.x86_64 that the syntax ENV a=b c=d with multiple assignments also works.

The https://docs.docker.com/reference/dockerfile/#env actually shows the ENV <key>=<value> as the preferred format and calls the ENV <key> <value> syntax an alternative one.

If the syntax with = and with support of multiple variables being set is actually supported by the software out there and expected to be supported, should https://github.com/containers/common/blob/main/docs/Containerfile.5.md be amended to at least show it as being a first-class citizen, if not the preferred one?