bug#43965: 27.1; An Introduction to Programming in Emacs Lisp

[Richard Stallman]

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  > "According to convention, you type two spaces after every sentence".
  > Recently a percentage of people have been using one space instead of
  > two to end sentences. Because it is a matter of preference, it would be
  > nice if one space is included in the regexes shown in this section.

That change would make the sentence commands give incorrect results.
There is a reason the regexp is what it is.

1. If you write two spaces between sentences, it is possible for
Emacs to distinguish sentence ends from abbreviations.  That regexp
is designed to do that.

2. If you write just once spaces between sentences, it is IMpossible for
Emacs to distinguish sentence ends from abbreviations.  No matter what regexp
you use, it can't do this job entirely right.

For users who want to have the sentence commands distinguish abbeviations
properly, there is only one way to get that:
(a) put two spaces between sentences, and
(b) use the current regexp, which matches only two spaces.

Your change would break case 1, and case 2 would still be broken
because case 2 is impossible.

If you want to use case 2, go ahead, but we will not break case 1!

-- 
Dr Richard Stallman
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)