I think we're going around in circles. Here's my existing experiment page: http://www.ghodmode.com/experiments/emsize.html
I'm going to do another one with more information. It's a square block, 1em wide and tall, with a lowercase 'm' inside it. I used Javascript (jQuery) to get the width and height of the block and the numbers it comes up with match what Firebug & friends say for the computed height and width. It shows that an em is as wide as it is tall, but it's not the size of the letter 'm'. Since the block's width is the same as its height, that shows that em is both a horizontal measurement and a vertical measurement. However, the letter doesn't fit, so an em isn't based on the size of a letter in the font specified... at least not the letter 'm'. more inline ... On Wed, Jan 25, 2012 at 6:28 AM, Tim Climis <tim.cli...@gmail.com> wrote: >> From my this, it really visually appears as if the em is not an "m" or an >> "M" in >> even the most plain typeface. That's when the text is centered. If it's left >> or >> right aligned, you can fit in two more "m". > > As has been discussed before in this thread, em is not a horizontal measure. > It is a vertical measure, and is defined as the size of the font. But a 1em block is a square. It's the same size vertically as it is horizontally. How can it be only a vertical measure, or only a horizontal measure? The problem is, it's not a measure of anything. It's relative to the font size, but none of the letters in the font are necessarily 1em tall or wide. This is the part I didn't understand before. > Directly from the CSS 1 spec (just to show that it's always been defined this > way - at least in CSS) "ems, the height of the element's font" > http://www.w3.org/TR/CSS1/#units You copied that from the comment in one of the example code blocks, not the actual description of the unit. It still leaves the question: How big is that? What it actually says is "The relative units 'em' and 'ex' are relative to the font size of the element itself." It doesn't go on to say how they relate to the font size. > The CSS 2.1 spec gets more precise, particularly in regard to x-height. > http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#length-units The CSS 2.1 spec does make it much clearer by linking to the font-size property definition. So, the 'em' is the font-size. But then it says "The 'em' unit is equal to the computed value of the 'font-size' property of the element on which it is used." That makes me ask "Huh?! How is it computed? How big is an 'em'?!" If they just took that word "computed" out of there, it would have been easier for me to understand. That's perfectly clear to some of you on this list? What I think it should say is that 1em is equal to the element's font-size. If the font-size isn't defined, the size of the em is equal to the user agent's default font size. -- Vince Aggrippino a.k.a. Ghodmode http://www.ghodmode.com ______________________________________________________________________ css-discuss [css-d@lists.css-discuss.org] http://www.css-discuss.org/mailman/listinfo/css-d List wiki/FAQ -- http://css-discuss.incutio.com/ List policies -- http://css-discuss.org/policies.html Supported by evolt.org -- http://www.evolt.org/help_support_evolt/
