@meme: Thanks fixed.
@adrian1944: I'd like a book sample that produces this error. Can you open a bug report and attach a file.
@HarryT: This is not simple to do, the problem is that CSS needs to be modified. In a conversion that can be done relatively easily as all the CSS is "flattened". But for arbitrary CSS the only way to do something like this would be to use an !important rule or set a style attribute on every <p> tag or something along those lines. The problem is CSS is too expressive, there are too many ways to specify a match, which makes modifying it non-destructively very difficult.
@jackie_w: An excellent point, I think I should be able to get the svg to use the original image dimensions fairly easily. I think I just forgot to do it while writing the code (Polish is a whole new code base, so it involved rather a lot of work). I'd appreciate it if you could open a bug report about it so I dont forget.
Regarding the name, yes the confusion with Polish is unfortunate, but in all other respects the name is perfect. Both Tweak and Modify are taken, and the rest are not quite a match. This function isn't about cleaning/tidying a book alone (though that may be one of its functions) but more about performing various tweaks to make the book look better, be smaller, more performant, etc.