Yes. I think we're agreeing. I was responding to this "Any binary allowed between the quotes.". Binary data can't generally be dropped directly into a text format without some kind of organized encoding.
Yeah, I think so… I thought they meant using a quote as a flag for “binary data lies ahead”, which really seemed odd to me. But — it is completely possible in a custom file type. But yes, if this case, the entire file wouldn’t be UTF8, even if all of the non-quotes data would be.
In retrospect, the idea of random binary data enclosed in quotes is what I’m mainly responding to — which I think we can all agree is a bad idea. (If you need to do that, encode it!)