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Re: Adapting Text Units: Spaces, paragraphs, and ems

From: Alastair Campbell <acampbell@nomensa.com>
Date: Wed, 12 Jul 2017 14:25:37 +0000
To: John Foliot <john.foliot@deque.com>, Laura Carlson <laura.lee.carlson@gmail.com>
CC: Greg Lowney <gcl-0039@access-research.org>, Jason White <jjwhite@ets.org>, Detlev Fischer <detlev.fischer@testkreis.de>, "w3c-wai-gl@w3.org" <w3c-wai-gl@w3.org>, public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
Message-ID: <8FD851EC-5072-4287-AC89-C14BB2FA0F1D@nomensa.com>
Hi John,

The testing on HTML based sites should be fairly easy, use styles and/or scripts to override the values to those in the bullets.

That’s what the bookmarklet [1] did (NB: needs updating to the newer values), so you apply that script and see what breaks or gets hidden.

VIP reader (for PDFs) takes a linearization approach, and you then add whatever font-adjustment you like. Testing there is pretty quick to, PDFs tend to either reflow ok, or implode fairly badly.

I’d suggest this:

* line-height (spacing) to at least 1.5 (space-and-a-half)
* spacing between paragraphs to at least 2 em (2 lines)
* letter spacing (tracking) to at least 0.12 em
* word spacing to at least 0.16 em

In HTML/CSS, line-height is the term, line-spacing elsewhere. If that is still confusing, then call it “1.5 em” which is then tied to the definition of font-size, and the same thing in practice.

For the paragraph spacing, browsers have their own padding/margin values which can vary, so it would be best to have a straight measurement (based on font-size) rather than adding to a default.

The original SC from COGA included: “Line spacing (leading) is at least space-and-a-half within paragraphs; and paragraph spacing is at least 1.5 times larger than the line spacing.”

I’m not clear what that means because it is relative unit multiplied by a relative unit?!

line height of 1.5 * 2 = 2.25 em?

I suggest we just round that off to “2 lines”, or “2 em”. If the requirement is for more, we can increase it but let’s do it clearly!



PS. Wayne has done some great work on how letter/word spacing, font-size, and font-family interact. It looks to me like we could combine the two width bullets into:
* letter spacing (tracking) to at least 0.05 em

1] https://github.com/w3c/wcag21/issues/78#issuecomment-277743607

From: John Foliot <john.foliot@deque.com>
Date: Wednesday, 12 July 2017 at 14:54
To: Laura Carlson <laura.lee.carlson@gmail.com>
Cc: Greg Lowney <gcl-0039@access-research.org>, Jason White <jjwhite@ets.org>, Detlev Fischer <detlev.fischer@testkreis.de>, WCAG <w3c-wai-gl@w3.org>, LVTF - low-vision-a11y <public-low-vision-a11y-tf@w3.org>
Subject: Re: Adapting Text Units: Spaces, paragraphs, and ems
Resent-From: LVTF - low-vision-a11y <public-low-vision-a11y-tf@w3.org>
Resent-Date: Wednesday, 12 July 2017 at 14:55

Hi Laura,

Thanks for this, it is indeed very nuanced.

Currently, we have a technique that also refers to 'spacing' but then provides examples using the CSS line-height property (see: https://www.w3.org/TR/WCAG20-TECHS/C21.html), which ultimately is what I believe we are looking for here.

As long as we can accurately convey the intent of this aspect of the requirement (it is a vertical measure we are seeking, not a horizontal one when it comes to spaces between lines and paragraph blocks) then I will be agreeable with a unitless measurement in the actual SC language (per existing convention), while at the same time noting that applications such as MS Word measure this unit as "lines":

[nline image 1]

Perhaps something like:

* line spacing (leading) to at least 1.5 lines (space-and-a-half)
* spacing between paragraphs to at least 2 lines (two spaces) larger than
the default line spacing

* letter spacing (tracking) to at least 0.12 em
* word spacing to at least 0.16 em

... (?)

From a testing perspective, I would envision something like first checking a page's CSS for the line-height property<https://www.w3.org/TR/CSS21/visudet.html#propdef-line-height> (which according to the spec can be expressed unitlessly, as an EM value, or as a percentage). At the opposite end of the scale, I could physically measure the actual height of the font / font-face in question and then, using that value multiply it by 1.5 to arrive at the second measure I need to test for (I don't advocate for this manual a test, but when push comes to shove...)


On Wed, Jul 12, 2017 at 7:25 AM, Laura Carlson <laura.lee.carlson@gmail.com<mailto:laura.lee.carlson@gmail.com>> wrote:
Hello John, Greg, Detlev, Jason, and everyone,

Based on Wayne's research and analysis, I previously suggest the
following for the Adapting text SC.

* line spacing (leading) to at least 1.5 (space-and-a-half)
* spacing between paragraphs to at least 2 (two spaces) larger than
the line spacing
* letter spacing (tracking) to at least 0.12 em
* word spacing to at least 0.16 em

On the call yesterday [1], some folks brought up that they felt the
use of "spaces" to measure leading for the Adapting Text SC is
untestable. At one point line-height was suggested.

Detlev, you were absolutely correct when you said, "if memory serves
line-height needs no unit". In CSS line-height is unitless. Eric Meyer
explained that in "Unitless line-heights". [2] It inherits from the
font size. This was discussed on in the Adapting text GitHub Issue
last March [3].

Moreover, WCAG 2.0 1.4.8 Visual Presentation [4] uses the "spaces" and
"paragraphs" for units. It states:

"...Line spacing (leading) is at least space-and-a-half within
paragraphs, and paragraph spacing is at least 1.5 times larger than
the line spacing..."

Is that currently untestable? If not, why not re-purpose that terminology?

As for using ems as a unit perhaps we need a definition because that
is a new concept for WCAG. How about something like:

em: A length unit relative to the font-size that is used. e.g., letter
spacing of 0.12 em means 0.12 spacing in addition to the default space
between letters of the font size in use.

Ideas for improvement? Other thoughts?

Thanks everyone.

Kindest regards,

[1] https://www.w3.org/2017/07/11-ag-minutes.html#item02

[2] http://meyerweb.com/eric/thoughts/2006/02/08/unitless-line-heights/

[3] https://github.com/w3c/wcag21/issues/78#issuecomment-288755938

[4] http://www.w3.org/TR/WCAG20#visual-audio-contrast-visual-presentation

Laura L. Carlson

John Foliot
Principal Accessibility Strategist
Deque Systems Inc.

Advancing the mission of digital accessibility and inclusion

(image/png attachment: image001.png)

Received on Wednesday, 12 July 2017 14:26:14 UTC

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