Re: Font Metrics concerns

I don't think defining an API for font metrics is the right place to start.
First off, you're really probably talking about some form of *line* metrics
rather than actual font metrics. A linebox can be affected by both font
metrics and other factors such as the variation in font-size across a line
and other content (e.g. an image larger than the line height).

Even knowing the fonts used for specific glyph runs across a line does
*not* give you the information needed for proper placement.

Example:

  font-family: Arial, sans-serif;

  <p>カレー毎日食べたい</p>

In this case the line metrics will be those of Arial and not the fallback
font used to display the Japanese characters in the run.

Example:

  <p>x<sup>2</sup></p>

Here the placement of x will *not* be purely based on the font metrics used
for the 'x' character but will be affected by the linebox height when the
synthetic superscript is taken into account.

Cheers,

John