When using expl3's ` \sys_if_engine_xetex:T` for xetex specific options, I inevitably get an error for `\setmonofont{Century Gothic}[SmallCapsFont={TeX Gyre Adventor:+smcp}]`. this happens even if `\ExplSyntaxOff is the first line of the T branch, happens if I sub the ` ` for `~` and I'm left to believe it's because of the `:`, is there a way to escape the colon, if the explsyntax cannot be turned off from inside?
Or am I just wrong on everything?