Posted by Jukka K. Korpela on 05/31/07 11:15

Scripsit Bernhard Sturm:

>>> Technically it's a measure of width (of an 'M') rather than of
>>> height.
>>
>> No it isn't.
- -
> Jukka: this is true in it's application, but Ben was talking about
> it's 'technical' origin.

No, as you can see from your own quotation, Ben claimed that the em _is_
"technically" a measure of width. That's plain wrong. A common
misconception, not a mortal sin, except perhaps if you actually base your
web site design on. Whatever the meaning of "technically" was, the statement
was false.

> Read a bit about typography (I am a typographer myself)

Would you believe that I have read a bit about typography and written about
it, too?

> The 'em' unit goes back to the Romans using the width of
> the letter 'M' to refer to the size of their letters...

That's what I explained in another message in this thread, emphasizing that
the connection was broken in ancient times. To be exact, the inscription
design used the em as the width of _some_ characters, including "M", but
surely excluding e.g. "I".

And it's just a little story, unless people misunderstand it as having some
impact on the em unit in CSS.

> Don't only look at how the 'em' unit is implemented in the CSS-specs,
> it's sometimes good to know the historical origin of things.

In this case, a little knowledge is just harmful. Historically, the em unit
was never a unit of width alone - only in conjunction with the height.
What's more important, knowing the history, or some distorted version
thereof, seems to make people think that the em unit _is_ the width of "M".

It's not a matter of "implementing" the em unit in CSS specifications. The
CSS unit is simply a reflection of a typographic tradition, in which the em
unit means the size of the font, not the width of anything.

--
Jukka K. Korpela ("Yucca")
http://www.cs.tut.fi/~jkorpela/

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