I want to produce two different outputs from the same music which has several bookparts. Tagging would seem ideal for this, but it seems that \keepWithTag is only valid within \score {}. Oddly, Frescobaldi's auto-complete allows me to type it both before the \book block and before the first \bookPart but then LP gives an error:
error: wrong type for argument 2. Expecting music, found #<Book>
Is there any way round this? I certainly don't want to have two different score blocks for each section.