Author is NetBSD developer. It is still favourite OS of mine when it comes to command line, text-only computer use. No one ever seems to acknowledge that plain text is the easiest to convert to any other format, while that is generally not the case for other formats. Maybe this is what is meant by "lowest common denominator". Perhaps a term like "most interchangeable format" would put plain text in a better light.
> easiest to convert to any other format I heard that a lot, but I feel like there are some very narrow assumptions involved. Could you give me some examples so I can better understand what people even mean by that? I am not even sure which other formats people think about in that context.
PDF by a mile. Copy / paste is usually an option, but not always. Sometimes I see embedded font tricks to prevent this. The copy goes well, but the paste is garbage due to the glyphs being indexed differently in the embedded font. For anything more than a trivial copy paste, the pasted text will include various extras that require some additional massage before the whole thing could be considered plain text.
Text contained in images. Early in computing I had a neighbor who would use low bit depth bitmaps to communicate with their family living in Asia. That solved all the common encoding problems from that time nicely. Thought it was clever.
These days, scanned documents and or people using images for more control over presentation are two common sources for plain text that just isn't.
For that matter, text on paper comes up a lot too. One has to run a program on it to recognize the text optically, or just type it in again.
These cases generally happen on a GUI too. Command line may be possible, but considerable skill and experience are required to make it happen without also investing more time and effort than the task seems worth.
All that said, my two preferred "general purpose" formats are plain text, like we are using here, and simple bitmap images.
Markdown is a format that can transport via plain text and that's great, but can get in the way depending. Same goes for CSV and the like. Normally, those are high value however. It all more or less survives a trip through, say Notepad or vi.
Same goes for the bitmaps making it through something like paint and it all being useful and displayable in a human readable form on most devices.
The moment it ends up in some application, the use value in that context may go way up because more things can be done and or done more quickly. The requirement for other parties to have the same software can and often does end up being a reason to render whatever it is into these two things.
For me, it boils down to whether it's read only, reference material, or if there is a need to extract parts of it, or process any of it in some fashion.