Here's the result of a quick hack, seems to do what I want. I changed the name to Temp Marker Enhanced, with version number back to 0,0,1 just so there aren't any unfortunate incidents with anyone thinking this is the latest official version of Temp Marker.
Changes from Temp Marker 1.2.1:
- Renamed to Temp Marker Enhanced - still copyright to kiwidude cos he did all the hard work
- Added 'Mark/Unmark all books by selected author'
- Added 'Mark/Unmark all books in same series'
- Handles multiple authors of a selected book, and empty series
- Can a book be in multiple series? If so, note I haven't tested this.
- Version now 0.0.1
Afficionados of plugin development may blanche when they see I've simply hardcoded the indexes into iterall() results to get the authors and series, but it works well enough for what I need at the moment anyway, and I don't know where to go to get documentation to tell me how to do it properly.
Use at your own peril, no warranty, etc.
Thanks to KiwiDude because without his efforts this wouldn't have only taken a few hours!