ideas? hell yeah! but i don't know how to convert my category_index.php (that was written for fb2) to work with fb3 as the structure changed slightly and a file named category.txt isn't necessarily available in fb3 to read out the category-data (that was placed within only one file named categories.txt in the old version) also all the subfolders have to be searched for images...
sorry but my coding-skill ends shortly below these requirements.
maybe someone could help to convert fb2's category_index ???
kind regards

Categories are sorted alphabetically by the filename of the directory — it's not the most elegant solution, but a quick workaround would be to name the directories alphabetically in the order you like, but add a category.txt file in each with it's correct name.

Ah ha! That's how to do it! I assumed that the category names were sorted by their name in category.txt (the visible name), so I never tried it. This is actually a pretty elegant way to sort categories exactly as you want. Thanks.