Posted by Ben C on 05/30/07 10:22

On 2007-05-30, Toby A Inkster <usenet200705@tobyinkster.co.uk> wrote:
> Ben C wrote:
>
>> Technically it's a measure of width (of an 'M') rather than of height.
>
> In traditional typography, yes. But the modern definition of an 'em' is
> that an em is the same as the font height.

Thanks, I didn't know that.

> The font height itself is quite a wishy-washy concept, but it can normally
> be thought of as the height of most capital letters and lower-case letters
> with ascenders (e.g. 'b', 'd', 'f', etc.). However, in certain fonts, some
> of these letters may be smaller or taller than the font-height.
>
> The CSS spec says that browsers are supposed to use the 1 em = font height
> definition.

Do you know where it says that? I have in 4.3.2 of CSS 2.1 "em: the
'font-size' of the relevant font". 'font-size' is hyperlinked to 15.7,
which says, "The font size corresponds to the em square, a concept used
in typography."

But you said that in traditional typography, em did mean width of 'M'.
So I am confused. In any case it says "em square" which implies no
distinction between width and height. Are Ms always square?

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