Code:
//echo -s $regsub(abc,b,[color:red]\[/color],%test) -> %test
//echo -s $regsub(abc,b,[color:red]\\[/color],%test) -> %test
//echo -s $regsub(abc,b,[color:red]\\\\\\\[/color],%test) -> %test

All echo "0 -> abc" where I hoped at least one of them would give me "1 -> a\c" or something like that.

However, if replace text is \\f or .\\ or anything that just does not consist entirely of backslashes, it gives the expected result of \ -> nothing and \\ -> \

I know a workaround, but that's not the point, is it?
Code:
//echo -s $regex(abc,^(.*?)b(.*)$) -> $regml(1) $+ \ $+ $regml(2)