Role of words "mulled" and "biocontainers"

I'm trying to decide how to think about mulled and biocontainers and about how to expose it to planemo users. In my head - "mulled" is a build tool that builds "biocontainers". I'm not sure it is worth the cognitive load to expose both to tool developers however. For instance, should

```
$ planemo test --mulled_containers
```

be

```
$ planemo test --biocontainers
```

And should

```
$ planemo mull
```

be something like

```
$ planemo biocontainer_build
```

Ping @bgruening in particular but I'd like to hear advice from someone more removed as well.