Is it always best practice to not include text punctuation in inline math mode?

Question

It has been pointed out on this site, e.g. here by egreg, that text punctuation doesn't belong to the formula in inline math. I've been following this practice for a long time, so I write for all $v\in V$, where ... as opposed to for all $v\in V,$ where .... However, the first version prevents kerning between V and the comma. Note that the comma is a lot closer to the V in the second version:

\documentclass{article}
\begin{document}
$v\in V$, where \quad $v\in V,$ where 
\end{document}

Note that there's no difference between the two versions if I replace V with A:

Now I'm wondering: Should I start including punctuation in my formulas to enable proper kerning, at least as long as fonts are used where the text and math punctuation glyphs look the same? Or are there reasons why the kerning is not desirable anyway?

Answer 1

If you want to maintain the kern but still keep your math expressions logically pure of sentence punctuation, and practically available for use in a document class that uses different text and math fonts, you could add a hand correction after the math, but in practice I'm not sure you'd want to do this:

\documentclass{article}
\def\kn#1#2{{\sbox0{$#1#2$}\sbox2{$#1{}#2$}\kern\dimexpr\wd0-\wd2\relax}#2}
\begin{document}
$v\in V$\kn V, where \quad $v\in V,$ where 
\end{document}

Answer 2

(updated the code to ensure that the Lua function doesn't perform string substitutions inside verbatim-like environments)

Here's a LuaLaTeX-based approach. It combines the \kn macro from David Carlisle's earlier answer with a Lua function (assigned to the process_input_buffer callback) that scans the input stream and automatically replaces all matches of <Upppercase Letter>$<punctuation mark> with David C's code. The Lua function may be switched on and off via the LaTeX macros \adjustcommaOn and \adjustcommaOff.

The application used in the following code is inspired by this question, which was closed as a duplicate of the present question. Note that the Lua function suspends its operations if LaTeX is inside verbatim-like environments such as verbatim, Verbatim, and lstlisting.

\documentclass{article}
% cf. https://tex.stackexchange.com/a/101059/5001:
\def\kn#1#2{{\sbox0{$#1#2$}\sbox2{$#1\mkern0mu#2$}\kern\dimexpr\wd0-\wd2\relax}#2}

\usepackage{luacode,geometry}
\begin{luacode}
in_verbatim = false
function ajust_punctuation ( s )
   if string.find     ( s , "\\begin{[vV]erbatim}" ) 
      or  string.find ( s , "\\begin{lstlisting}" ) then
          in_verbatim = true
   elseif string.find ( s , "\\end{[vV]erbatim}" ) 
      or  string.find ( s , "\\end{lstlisting}" ) then
          in_verbatim = false
   elseif in_verbatim == false then
      -- scan for "<UppercaseLetter><$><PunctuationMark>" pattern:
      s = string.gsub ( s , "(%u)%$(%p)", "%1$\\kn %1%2" ) 
   end
   return s 
end
\end{luacode}
\newcommand{\adjustcommaOn}{%
    \luadirect{luatexbase.add_to_callback(
   "process_input_buffer", ajust_punctuation, "ajust_punctuation" )}}
\newcommand{\adjustcommaOff}{%
   \luadirect{luatexbase.remove_from_callback(
   "process_input_buffer", "ajust_punctuation" )}}

\setlength\parindent{0pt} % just for this example
\obeylines 

\begin{document}

Proper spacing: $A$, $E$, $Q$, $R$. 
\adjustcommaOn
Proper spacing: $A$, $E$, $Q$, $R$. --- Virtually no change.

\smallskip
\adjustcommaOff
Acceptable spacing: $B$, $C$, $D$, $G$, $O$, $S$, $Z$. 
\adjustcommaOn
Acceptable spacing: $B$, $C$, $D$, $G$, $O$, $S$, $Z$. --- A little bit better.

\smallskip
\adjustcommaOff
Poor spacing: $F$, $H$, $I$, $J$, $K$, $M$, $N$, $P$, $T$, $U$, $V$, $W$, $X$, $Y$.
\adjustcommaOn
Poor spacing: $F$, $H$, $I$, $J$, $K$, $M$, $N$, $P$, $T$, $U$, $V$, $W$, $X$, $Y$. --- A major improvement.

% Note that "\adjustcommaOn" is in effect.
\begin{verbatim} 
Proper spacing: $A$, $E$, $Q$, $R$.
Acceptable spacing: $B$, $C$, $D$, $G$, $O$, $S$, $Z$.
Poor spacing: $F$, $H$, $I$, $J$, $K$, $M$, $N$, $P$, $T$, $U$, $V$, $W$, $X$, $Y$.
\end{verbatim}
\end{document}