Re: [css3-values] Physical length units

On 2012/02/21 19:52 (GMT) Matthew Wilcox composed:

> Felix, it sounds like you're arguing designers should never set font
> size/line height on<html>?

With the usual reservations on the use of the word "never", and WRT size, 
absolutely. Those needing to support old IE versions need to "set" 100% on 
html and/or body in order to avoid one of its worst and well known bugs. And 
there are situations where the designer has complete knowledge and/or control 
over the hardware and viewing environment, e.g. POS kiosks or classrooms. But 
outside a limited set of special cases, deviating from the browser default 
size at the base level (body and/or html) needs to be considered a major 
first level no-no. It should be a top priority in WCAG rather than missing 
virtually altogether.

Executive summary:
Web designers need necessarily be free to contextually size similarly to 
designing for print, but visitors' defaults normally must define the context 
- the base size, which necessarily is 1em/medium/100%, as long as respecting 
visitors is the right thing to do. Setting some other size on body or html is 
antithetical to this priority.

Line-height, while not altogether unimportant, plays a rather small role in 
legibility or reading comfort when text is comfortably sized. More leading 
when lines are longish certainly can be helpful, but usually the better fix 
is to adjust the lines, not diddle with leading, and certainly not to make it 
resemble a middle-schooler's double spaced term paper. Most web font 
designers really have done a decent job setting default leading for their 
fonts when they are used in lines of reasonable length at a comfortable size.


For a sighted visitor audience, legibility is job one. Period. To anyone who 
can't read text comfortably, nothing else a designer's CSS can or can't do to 
the end of maximizing legibility matters more than ensuring the user's 
preference for base text size be respected.

Setting some size other than medium/1em/100% at the root level is telling the 
visitor he doesn't deserve your respect, that the designer somehow knows 
better than he or the supplier of the unpersonalized environment he's using 
that his presumptively perfect default font size isn't.

The print world and the web each have their strengths and their weaknesses, 
some of which overlap, some which don't:

Overlap:
The designer gets to choose the spatial relationships, how big the figure is 
compared to the paragraph, where foo goes in relation to bar, how many words 
make an appropriate line length, whether menus go to one side or over the top 
or even to have any, how many columns, how much smaller "fine print" or 
superscripts, how much bigger main heading and subheadings, whether caption 
text or blockquotes should be oblique or monospace or a different face or 
size than paragraph text, etc.

Differences:
Print: once it's done it's done. Little to no adaptability is possible short 
of complete redesign, certainly not instantly.

Web: Powerful powerful advantage in natural built-in adaptability of the 
_user_ agent to conform content to the users' environments. Those who don't 
read books, newspapers or magazines because they only come in one size are 
not so limited on the web. Web users get to personalize their personal 
computing devices, and make things bigger if that's how they like them or 
need them, or smaller if that's their preference. And even after they've done 
that personalization, the user agents will nevertheless continue, if 
unconstrained by designer styles, to adapt the content to fit the space 
actually available. The web could be a panacea if only web stylists weren't 
insistent on using CSS to make web pages look like Sears catalog pages, 
pharmaceutical ads in magazines or miniature TV commercials.

Designer knows how big the paper, billboard, kiosk or jumbotron is.
vs.
Designer has no way to know most of the many variables that go into how big 
the visitor needs or wants things to end up:
	actual device pixel density
	physical viewport metrics
	viewing distance
	visual acuity
	backlighting
	ambient light
	health or other chronic distractions

Remember too that the difference between a default size change and a zoom 
level change differs rather little. The most obvious difference is temporal, 
that is, default is done in advance. The other is that it's applied globally. 
Zoom is done after the fact, a defensive measure applied when an offense is 
encountered. WRT text-only zoom, usually there's no apparent difference in 
effect of zoom application vs. default effect on layout in maximally 
compliant browsers. Saying zooming needs to be embraced without saying 
default size needs be respected is like saying it's OK to sell peaches by the 
pound but not oranges because oranges need to have their noxious skin removed 
before eating while peaches don't, an orthogonal distinction.
-- 
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)

  Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata  ***  http://fm.no-ip.com/

Received on Wednesday, 22 February 2012 02:48:20 UTC