Since Regular Expressions may be a bit complicated it may help
to have some examples for usage with FILE-REN.VDM.

1) Renaming all .txt files to .doc files

       Old name: {.*}.txt
       New name: \1.doc

2) Renaming all .txt files to .doc files with additional name modification.
   The leading text "test" should be renamed to "prod"

       Old name: test{.*}.txt
       New name: prod\1.doc

3) Files named like abc567.txt should be renamed to DATA-567.abc

       Old name: {[a-z]+}{[0-9]+}.txt
       New name: DATA-\2.\1

4) Add an additional digit to numbered files  (Patrick Carroll's task)

       Old name: {.* }{[0-9][0-9]}{[we]_}{.*}.jpg
       New name: \10\2\3\4.jpg
  
       Example:
       IL03 016s 10w_001.jpg   -->    IL03 016s 010w_001.jpg
       IL03 025n 015e_001.jpg  (untouched)

5) to be continued ...