I'm giving up on this topic. After reading the specs numerous times, I'm realizing that the specs themselves are circular. I feel like I'm trying to find out if the chicken or the egg came first.
On ems and exes: http://www.w3.org/TR/2011/REC-CSS2-20110607/syndata.html#length-units :" em: the 'font-size' of the relevant font. It may be used for vertical or horizontal measurement. (This unit is also sometimes called the quad-width in typographic texts.)" "ex: the 'x-height' of the relevant font" "If reliable font metrics are not available, UAs may determine the x-height from the height of a lowercase glyph. " On font-size: http://www.w3.org/TR/2011/REC-CSS2-20110607/fonts.html#propdef-font-size: On all other properties, 'em' and 'ex' length values refer to the computed font size of the current element. em = font-size = em = font-size = em = font-size === paceaux wants to finger paint </email> <signature id="paceaux"> @paceaux </signature> On Jan 25, 2012, at 3:04 AM, Ghodmode wrote: > 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/ ______________________________________________________________________ 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/
