Sorry for the late replies, been distracted by doing Sigil development the last few weeks and that is taking 100% of my time...
@unboggling - I wouldn't hold high hopes for ISFDB from the briefest of looks, given the highly unstructured way they dump data out on their pages. Though you (or anyone else) has the tools with this plugin to do exactly the same experimenting as I would do - so if you figure it out I will include it in the predefined settings.
@Pepin - you seem to be rewriting your posts a lot
. You had a question previously asking for a "Select all matched" button, which I thought was a reasonable idea, if people wanted to focus only on the books they don't have on a list and delete the ones they do. So I can add that at some point.
As for custom columns, I decided against it (for now at least) a while back in this thread. One of the problems is the UI - you can see how busy the web page settings tab is already, trying to add extra xpath expression sets in there all starts to get very messy. And then there is all the data validation etc that would have to happen to allow calibre to save it, the extra columns of data on the Step 2 screen etc. I'm not saying "never" on it because it would be useful in some circumstances to get around the limitation in calibre's metadata download functionality of being unable to scrape into a custom column. However I would rather that limitation was fixed first, and then we see realistically what use cases still exist which would justify the huge effort required to add to this plugin.
I really should release this, the only holdup has been the lack of enthusiasm for trying to write the instructions on how to *fully* use it in a hopefully clear fashion. Perhaps in a few weeks when my Sigil todo list shrinks, obviously it is fully functional for people to download above, just rather hidden...