bug#63398: 28.2; Doc or behavior of replacement commands (e.g. `replace-string')

[Juri Linkov]

>> The rules of replacement case-folding are more complex than documented.
>> `replace-match' checks if the initial is a caseless word constituent
>> like "0", and treats that like a lowercase initial.
>>
>> So  "test a → test b" replaces "Test A" with "Test B",
>> but "test 0 → test 1" replaces "Test 0" with "test 1".
>
> Can we fix this?  Should the behavior be changed?

I guess the default should never change.
But maybe the rules could be customized.

> Should the behavior remain like this and the doc
> be changed?

The current implementation of rules is quite complex.
No sure if all details can be documented succinctly.