[css-text-decor] line-decoration averaging or not

We discussed at the F2F requiring the decorating element to set the
position and thickness of the line, ignoring descendant content.
This is acceptable for underlines on alphabetic-aligned text,
however it doesn't work for centered text, which is the most common
alignment in vertical writing modes.

       []
       []
       []
      +--+
      |  |
      +--+
      |  |
      +--+
      |  |
      +--+

An underline positioned to the smaller text will cut through the
larger text. (We have a similar problem with overlines, however
they are less common.)

David argues that allowing descendants to affect the underline
position means underlines may be slightly inconsistent across
similar elements. However, I think it's a bigger problem if
they sometimes cross through text than if they sometimes aren't
pixel-perfect.

If we're unsure about the behavior we agreed to spec last fall,
then I suggest that we mark the positioning and thickness
undefined, as it is in CSS2.1, take this level to CR, and figure
out exactly what rules we want in L4. I don't think it is a good
for an underline to strike through the text of a descendant whose
only crime is having a larger font-size, and I do not want our
specs to require it.

Proposed text for undefining:

   "The exact position and thickness of line decorations is
    UA-defined in this level. However, the UA must use a single
    thickness and position on each line for the decorations
    deriving from a single decorating box."

Unlike the CSS2.1 text, this doesn't even give any suggestion
of how to resolve the positioning.

~fantasai

Received on Tuesday, 25 June 2013 19:39:14 UTC