% engine=luatex

\starttext

Let's see what sort of spaces \CONTEXT{} puts before interrogation marks in
{\em frenchpunctuation} character spacing mode:\blank[small]

{\setcharacterspacing[frenchpunctuation]a? aa? aaa? abba?}

\blank[big]

If we hardcode the thin space, it's a bit shorter:\blank[small]

a\,? aa\,? aaa\,? abba\,?

\blank[big]

Here we use the font's glyph for U+202F {\sc narrow no-break space} and we see
nothing: Latin Modern doesn't have a glyph for it.\blank[small]

a\char"202F? aa\char"202F? aaa\char"202F? abba\char"202F?

\blank[big]

Now we override Mark IV's default settings, see {\tt core-spa.mkiv}\blank[small]
\unprotect
\setupcharacterspacing [frenchpunctuation] ["003F] [\c!left = .16667,\c!alternative=1]
\protect

{\setcharacterspacing[frenchpunctuation]a? aa? aaa? abba?}

\stoptext
