bug#52558: Option for easier typing of regexps

[Juri Linkov]

>> >> +(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.
>
> I don't think this is enough.  First, the first sentence of the above
> doc string doesn't have any such reference, so Apropos commands, which
> show only the first sentence, will not have that reference.

But "isearch-regexp-function" is too long for the first sentence.

> And second, the doc string of isearch-regexp-function says nothing
> about replacements.

It should say nothing about replacements.  This is explained
in the second sentence:

  `isearch-regexp-function' is bound to it when searching
  for a string to replace.