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

We’re not being technology agnostic here.  The truth is that the only reason we are drawing a difference between em units and a unitless factor on the font size is technology-specific to CSS.  In reality they are exactly the same, i.e. for the current element:

`Line-height: 1.5` = `line-height: 1.5em`

The problem is that these are inherited properties, so a length value in em passes the same computed length to children, while the factor becomes a factor on the child’s font size.  Obviously the latter is usually the desired behavior.  Why the CSS standard doesn’t also allow factors to be used for `letter-spacing` and `word-spacing` is a good question.

So, to be totally technology agnostic here, we ought to pick one and be consistent.  Given the confusion that could arise by specifying inheritance with em units, I’d strongly vote for the following:

1.       line height (line spacing) to at least 1.5 times the font size

2.       letter spacing (tracking) to at least 0.12 times the font size

3.       word spacing to at least 0.16 times the font size

We can explain what this translates to for CSS in Understanding, which is advantageous in case things change.


From: Alastair Campbell []
Sent: Wednesday, July 12, 2017 12:17 PM
To: John Foliot <>
Cc: Laura Carlson <>; Greg Lowney <>; Jason White <>; Detlev Fischer <>;; public-low-vision-a11y-tf <>
Subject: Re: Adapting Text Units: Spaces, paragraphs, and ems

That’s fine for me, thanks.

Any objections? Going, going…


From: John Foliot

Hi Alastair,

A bit more fine-tuning... how about:

* line-height (spacing) to at least 1.5 em (space line-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



Received on Wednesday, 12 July 2017 17:29:35 UTC