Backreferences in rex.gsub

[Jamuse <jamuse@...>]

I'm trying to access a backreference (via %1) captured in parenthesis, as shown below:

 value = rex.gsub(value, "(?:(.{2,})%1{32,})", "x", nil, 0, 0);

What is the correct syntax for accessing captured data in rex.gsub?

Thanks,

 - J