Comments on Fonts module

I've got a few comments about the last call on the Fonts module.

a) Note 1 in section 3.4 reads: "To preserve readability, an UA applying these guidelines should nevertheless avoid creating font-size resulting in less than 9 pixels per EM unit on a computer display"

Specifying "9 pixels per EM" doesn't account for superscript characters. Since these are usually rendered at a size of less than 1 EM, simply following this rule and allowing text to be rendered at 9 pixels will likely render superscript and subscript characters unreadable. This should be accounted for by an addendum to the note, or by changing the wording to be simply "...avoid rendering any character less than 9 pixels high on a computer display"

Also, specifying a minimum of 9px is sufficient on most of today's displays, but once LCD displays are commonly available with a DPI of 200, 300, or more, 9 pixels will be unreadable. An additional admonition should be added, stating that no character should be rendered less than x fraction of an inch high (perhaps based on the x-height, or tied in with font-size-adjust?). I'm not sure what value this fraction should be, but it will be necessary.

The module should also recommend that user agents attempt to discover the actual DPI of the display, instead of assuming a fixed value of 72px or 96px. An os-level API is available under Windows to do this, and likely through other OSes as well.


There's a typo in this sentence:
For example, the popular font Verdana has an aspect value of 0.58; when Verdana's font size [is] 100 units, its x-height is 58 units.