[Hadrien]

Originally Posted by Jellby

While that is true, I think it's also desirable that the reading system has a way to override a book's settings. I'll try removing the text-align from the epub css and putting it in the index.css (to be used only with a web browser)

I disagree: overriding a book CSS can be very difficult. The best situation would be for publishers to avoid styles that shouldn't be necessary, this way it would be much easier for the reading system to handle everything.

Some styles might be absolutely necessary to display part of the text and in this case, shouldn't be overrided.

I really believe that we need to issue best practices regarding this issue. I mentioned this among other problems to the working group:

Thanks to CSS and embedded fonts, publishers can create some very nice looking books in EPUB. But for most consumers, e-books are fantastic for another reason: unlike paper-books, they can select how everything is displayed. Based on my experience, users love to customize the following things:
- Font Family
- Font Size
- Margins
- Line Spacing
- Paragraph Spacing (https://www.mobileread.com/forums/showthread.php?t=31316)
Let's take the example of the font family.
I just got a new book, and for some reason, I find that the embedded font is quite difficult to read. Unfortunately for me, it might be difficult for the reading system to switch to a different font, based on how CSS is used.
There's usually 2 different situations:
- a font is defined as the default font for the book
- a font is used for specific parts in the text (headers for example)
In the second situation, the reading system should require me to use the font, while in the first one, I should be able to override the CSS settings and use my own font if I'd like. Unfortunately, most of the time, the font will be declared the same way, and it'll make things very complex for the reading system.
A best practice would be to declare the fonts in a different way. For example, reading systems could be allowed to override the default font families (serif, sans-serif, monospace...) while custom font families would always display the embedded font.
I really believe that we could find the right balance between what a publisher recommend a book to look like and what a user is allowed to modify, but we need to define a set of best practices, otherwise it'll be nearly impossible for a reading system to handle this.