>> \def\quark\quark{\quark} > > with error message "Use of \quark doesn't match its definition" if it's ever > accidentally executed. I *think* this definition still fulfils the use case > for quarks themselves, but I wonder if it would involve a little too much > code shuffling to be worth implementing for expl3. > > (And it makes it more difficult to peek inside a quark, if that's ever > necessary.) > > Before I forget about this idea, does anyone have any comments on the > matter? Hi Will, if I understand correctly, quarks are meant to work in cases like \def\foo{#1} \ifx\foo\quark ... \else ... \fi This requires quarks to be defined as expanding to themselves. Or it requires to distinguish between a quark and a token list containing that quark. I personally don't use quarks as anything else than delimiters, so any definition is fine, but I guess that property of quarks is used in constructions like \tl_set:Nn \foo {#1} \quark_if_recursion_tail_stop:N \foo or \prop_get:NnN \foo {key} \bar \quark_if_no_value:NTF \bar { } { } This could be solved by altering quark tests, perhaps...? Regards, Bruno