Re: [css-masking] mask-box-slice: fill definition

On a related note,
   # The middle image part is discarded (treated as fully transparent
   # black) unless the fill-box keyword is present.

This means that by default, the padding box of the element is
masked out (not shown).

I think that's the opposite of the intended behavior. :)
By default, the middle part should be shown, not masked out.

~fantasai