Hi
I've got a little problem with MP3TAG v2.38
I would like to have a track filename like: Artist - Title (Feat.).mp3
Problem is that my track filename is like that: Artist - Title Feat."leading space".mp3 and without the () "Parenthèse??" aren't present at the beginning and at the end of the Featuring...ggrr 
After reading the FAQ and trying by myself i didn't succed yet...
There my "New Action":
Action type: Replace with regular expressions
Field: _FILENAME
Regular expression: ^Feat.\s+$
Replace matches with: (Feat.($1))
And is there a FAQ that explain every % $ \s $num ,etc... signification step by step in order to do learn and do a personnalized script?
Thanks a lot for your help & sorry for my poor english i did my best 
One solution could be:
Regular Expression: (Feat.)(.*)(.mp3)
Replace matches with: ($1$2)$3
I'm sure, this is not the best possible solution, but you can change it as you like.
As always: Don't try it on your original mp3. Make some backup first. 
Thank you for your fast answer!
Regular Expression: (Feat.)(.*)(.mp3)
Replace matches with: ($1$2)$3
It works but it's a bit slow in mass rename because as the action change/replace the extension .mp3 by the same .mp3 on the filename, it seems that it's makes the operation more longer than a modification on tags only! But perhaps i'm wrong 
So i did that and the file file keep almost the .mp3 extension:
Regular Expression: (Feat.)(.+)[^mp3]
Replace matches with: ($1$2).
But it strange because i was forced to keep the dot in the "replace matches line" because if not the action delete the last character or number before *.mp3 and don't include it in the parenthese
Do somebody help me to resolve this? 