How to use the --def exts=pattern option?

[cheaters]

Advanced Options:
--def exts=pattern override default pattern for what extensions will be cleansed
--def terms=pattern override default pattern for for what paths will be cleansed

Would you please show the syntax for the "pattern" if you wanted more than one item to be removed. Something like this? {.sub, .idx, .txt}

Would this be the best script to recursively remove every subtitle that does not contain ".eng"?