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

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:, 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":

[image: Inline 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
<> (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 <>

> 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,
> Laura
> [1]
> [2]
> [3]
> [4]
> --
> Laura L. Carlson

John Foliot
Principal Accessibility Strategist
Deque Systems Inc.

Advancing the mission of digital accessibility and inclusion

Received on Wednesday, 12 July 2017 13:55:23 UTC