Using \@-ified punctuation while using \frenchspacing

Question

After reading this very informative TeX.SE thread about spacing and punctuation, I was left wondering about an issue that didn't seem to be addressed: using \frenchspacing together with the modified punctuation \@., \@?, etc.

As far as I can tell visually, using \frenchspacing together with these commands works correctly (i.e., it seems like nothing breaks, and the extra space is suppressed as normal), but are there problems that can arise from doing so?

Moreover, when using \frenchspacing, "should" I still use \@. and its friends where it would ordinarily be necessary, in case someone wants to remove \frenchspacing later? Would accommodating (hypothetical) future editors in this way be "standard", "above and beyond the call of duty", or "crazy"?

Answer 1

The definition of \@ is simply \spacefactor 1000, so based on TeX's rules, no extra space will be added after .\@, while it will after \@. (if \nonfrenchspacing is in force).

The definition of \frenchspacing is just to set the \sfcode of all punctuation signs to 1000, so there will never be additional space. Therefore the action of \@ in a \frenchspacing regime is void. But it doesn't harm either.

If you fear that your text can be reverted to a \nonfrenchspacing regime, then use it. Otherwise it's completely unnecessary.

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Actually in some cases it can do damages: amsthm redefines \frenchspacing in order to use the space factor for deciding whether a punctuation sign is present. However this is hidden in macros, so it would be difficult to add a \@ that makes things go wrong.