[CSS21] Empty line boxes should be mentioned in 10.8

Hi,

Section 10.8 of CSS 2.1 states that the line-height property defines the 
minimal height for every line box. However, the ninth paragraph of 
section 9.4.2 states that empty line boxes are to be treated as 
zero-height or non existent.

Both statements seem to be contradictory. I think that the exception of 
empty line boxes (with "empty" as defined in 9.4.2)  should be mentioned 
in 10.8.

Regards,
-- 
Simon Sapin