It can work with proportional fonts. Word for instance defines it well enough to be useful. Rather than down taking you to the same column on the next line, it just takes you to the character rendered at a similar x coordinate on the next line.
I'd use such a feature if I had to fill a table, and wanted to move to the same column on a different row. But with proportional fonts, the columns don't line up. So yes, it can move to the same x coordinate, but why is this useful?
It's useful for general text navigation, and writing code is an instance of that.
> I'd use such a feature if I had to fill a table, and wanted to move to the same column on a different row. But with proportional fonts, the columns don't line up. So yes, it can move to the same x coordinate, but why is this useful?
"Doesn't work well for use case X" != "not useful [in general]"
If your text is laid out assuming fixed-width fonts, and it's important for you to move to the same column in a different row, then just use fixed-width fonts and the method I described would work as you expect.
Acme is opinionated and it’s a good thing if it fits its userbase. I am actually quite fond of many design decisions and maintain patches to workaround defaults that could drive me insane.
My personal feeling is negative on this matter, just as if I would need to reach to the mouse to delete a character. Up and down mapped to something like page up / page down feels as infuriating as those website that hijack scroll and back button.
Up and down can't work, because acme was designed for proportional fonts, and many of us acme users use proportional fonts. Up and down are not well defined/not useful with proportional fonts.