sort --key-debug

[Pádraig Brady]

I find it quite difficult to determine correct key positions to use,
especially given the complicated rules for (global) -b options etc.

I wonder would it be useful to add a --key-debug option,
which would mark in the output the keys used.

For multibyte locales you could use: ⌜key1⌟ blah blah⌜ key2⌟
or for single byte locales:          «key1» blah blah« key2»
or for ascii:                        (key1) blah blah( key2)

It might mean that users would not have to reference the
detailed documentation as much. Note the above markings don't
capture key order or type, but the bounds are what I find
trick at least. I suppose you could add order, and support
overlapping keys with: ²key₂ blah blah¹ key₁

I'm not sure about this at all, I'm just thinking out loud really.

cheers,
Pádraig.