Re: Baselines (was RE: Units, font sizing, and zoom suggestion for CSS 3)

Karlsson Kent writes:
> The following baselines should be maintained for all text:
[...]

There's currently text in the works in the CSS WG to specify these
various baselines. The definition of 'vertical-align' may have to be
re-interpreted to deal with texts that mix scripts.

One part of the solution appears to be to define a property
'baseline-identifier' which specifies what the "dominant" baseline of
a piece of text is. If 'vertical-align' has the value 'baseline' (the
initial value), the text will then be aligned on whatever is the
dominant baseline for that text. Other values of 'vertical-align' are
stil available to move the text up or down from this default position.

For a formula and a Japanese quote, you could set, resp.:

    MATH { baseline-identifier: mathematical }
    Q[LANG|=jp] { baseline-identifier: ideographic }

In fact, similar definitions should probably be in the browser's
default style sheet, so the designer almost never has to specify them.

    Property: baseline-identifier
    Values:      top | middle | bottom | ideographic | lower | hanging
                 | mathematical | inherit
    Initial:     lower
    Applies to:  inline elements
    Inherited:   yes
    Percentages: N/A
    Media:       visual

(Another name for 'lower' could be 'latin', because 'ideographic' is
actually lower than 'lower'... On the other hand, 'lower' isn't just for
the Latin script.)

Chapter 15 of CSS2[1] already describes the various baselines (though
maybe not complete), but in CSS2 they aren't used for the
'vertical-align' property.

In combination with this, there is also a proposal for a
'line-height-policy' property that can, among other things, enforce a
mode in which the line height throughout a paragraph remains constant,
despite text with different baselines or sizes.

[1] http://www.w3.org/TR/REC-CSS2/fonts.html



Bert
-- 
  Bert Bos                                ( W 3 C ) http://www.w3.org/
  http://www.w3.org/people/bos/                              W3C/INRIA
  bert@w3.org                             2004 Rt des Lucioles / BP 93
  +33 (0)4 92 38 76 92            06902 Sophia Antipolis Cedex, France

Received on Thursday, 3 February 2000 13:09:57 UTC