@REREPLACE[source_re,target_re,source] - Regular expression back reference replacement.

 

source_re - Regular expression to apply to the source

 

target_re - Regular expression for back reference

 

source - Source string

 

Example:

 

To replace the input string "a1.txt" with "1a.txt":

 

@REREPLACE[(.)(.)\.txt,\2\1.txt,a1.txt]