Having trouble thinking about mmm mode & friends

[Skip Montanaro]

I have an application where mmm-mode, polymode, or something similar might
be useful. I'd like to mix Python, Markdown, and JSON or YAML. I did a bit
of doc reading last night but came away with no idea how I would set things
up. Are there markers between chunks of a given mode? How do I declare to
whatever multi-mode system I choose that these are the three modes?

I'll keep reading, but would appreciate pointers to something more basic
than the mmm-mode and polymode docs I've already found.

Thanks,

Skip Montanaro