Regular expressions in Bulk Rename Utility are imperfect. Here are some examples of regular expressions that give wrong result in BRU.
Assume that input name is: Example.S02E34.Temporary.File
Match: S02
Replace: xxxxx
Correct result: Example.xxxxxE34.Temporary.File
BRU wrong result: xxxxx
Match: S02.+
Replace: xxxxx
Correct result: Example.xxxxx
BRU wrong result: xxxxx
Match: .+S02
Replace: xxxxx
Correct result: xxxxxE34.Temporary.File
BRU wrong result: xxxxx
Match: le
Replace: xxxxx
Correct result: Exampxxxxx.S02E34.Temporary.Fixxxxx
BRU wrong result: xxxxx