Allow any argument like `**kwarg`

[njzjz]

In dpdispatcher, env argument allows any sub-arguments. We may consider to add a new class like AnyArgument to handle this situation.

[y1xiaoc]

Sorry I didn't check this. Will an Argument with dtype=dict and no subfields do the work?

[njzjz]

I don't think it will work for argchecking... right?

[y1xiaoc]

Just added an example in test. Is this able to do the thing?

[njzjz]

Just added an example in test. Is this able to do the thing?

No. I got the following error:

dargs.dargs.ArgumentKeyError: [at location `envs`] undefined key `aa` is not allowed in strict mode

[njzjz]

Although it works in the normal mode, it won't work in the strict mode.