> + \ifx\indexsortkey\empty > + \message{Empty index sort key near line \the\inputlineno}% > + \xdef\indexsortkey{ }% > + \fi > > Do you think this would help fix this kind of problem?
Yes, thanks. Maybe it makes sense to also emit Are you trying to index a backslash while `@set txiindexbackslashignore` is active? This could be generalized to catch the other `txi*ignore` flags, too. Werner