bug#52558: Option for easier typing of regexps

[Juri Linkov]

> Thanks, but the doc string of the new function is hard to understand:
>
>> +(defvar replace-regexp-function nil
>> +  "Function to convert a search string to a regexp to replace.
>> +It's bound to `isearch-regexp-function' when searching
>> +for a string to replace.")
>
> The first sentence is unclear: what do you mean by "convert a search
> string to a regexp to replace"?  What "search string" is being
> converted to regexp, and how does "replace" enter this picture?

It has a reference to `isearch-regexp-function' that has
a complete explanation to avoid duplication of the docstring.

> And this:
>
>   It's bound to `isearch-regexp-function' when searching
>
> seems to be incorrect: it's isearch-regexp-function that's bound to
> replace-regexp-function, not the other way around.

Maybe this is better:

  `isearch-regexp-function' is bound to it when searching