I see the ticket has been fixed, and I saw the
changes you made in the core files. That said, I'm not quite sure how to leverage this in an input plugin.
First question is which file is actually considered the input plugin? Is it /calibre/ebooks/<format>/input.py? I see most folders there have an input.py, but not all.
And then finally what exactly do I need to define in an input plugin, do I need to define a function called HTMLPreProcessor in each plugin that acts similarly to pdftohtml?