Is there a way to specify a regex is case-insensitive in {rex}?

We are passing it to list.files(pattern=) so the normal arguments are not available -- the only approach would be to add (?i) AFAICT. Without it, the regex is substantially gnarlier:

rex(".", or(group(one_of("Rr"), or("", "html", "md", "nw", "rst", "tex", "txt")), "Qmd", "qmd"), end)
# vs (not exactly the same, but that's fine)
rex(".", ignore_case(or("r", "rhtml", "rmd", "qmd", "rnw", "rrst", "rtex", "rtxt")), end)