What is the difference between post-processor and post-processors?

What is the difference between post-processor and post-processors? I looked at post-processors - build - Blocks | Packer by HashiCorp but it doesn’t explain what the difference is.

I’m not sure why someone would use one versus the other.

@matt1

A post-processor can also take the Artifact from another post-processor when it is defined in a post-processors block list, that is a list of chained post processors.

I believe that’s the main difference. Otherwise, the produced artifact is not carried over to subsequent post-processors. A better example would be something like this: Artifice - Post-Processors | Packer by HashiCorp

So if I understand correctly, the only time the post-processors block is useful is when using artifice. Otherwise one can use a series of post-processor blocks and it will work fine.