Convert tags to filenames. Format string with 'if' function.

What I want to do is to write a format string which does this:

'%artistsort% (but if there is no data in this placeholder, use %artist%)'

What is the syntax I must use in order to maker this to happen?



Thanks. In the end, really straight forward

I should have looked properly in the help docs, or used my brain more. I'm getting lazy.