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Thread: EM vs. REM?

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From: deborah.kaplan@suberic.net
Date: Thu, May 30 2013 10:18AM
Subject: EM vs. REM?
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I'm currently working with our web designers to put together an
easy-to-use set of documentation for our workplace on
accessibility best practices for all of the different departments
that create websites. During the process, one of the web
designers has introduced me to the CSS3 "rem" unit:

http://www.w3.org/TR/css3-values/#rem-unit
http://www.css3files.com/2012/10/11/relative-is-the-new-absolute-the-rem-unit/

My usual advice up until this point has always been use EM
instead of PX for sizing, as a basic accessibility best practice.
I haven't seen anyone on any of the accessibility forms talk
about REMs. As far as I can tell from various websites I see
around, it seems to be getting primarily used by people who
resisted switching from pixel dimensions to relative at all, as a
more comfortable way of switching. Is there accessibility best
practice about when to use REMs?

Thank you so much,

-Deborah Kaplan
--
Accessibility Team Co-Lead
Dreamwidth Studios, LLC

From: Jukka K. Korpela
Date: Thu, May 30 2013 10:37AM
Subject: Re: EM vs. REM?
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2013-05-30 19:18, = EMAIL ADDRESS REMOVED = wrote:

> I haven't seen anyone on any of the accessibility forms talk
> about REMs.

There isn't much to talk about it, since it adds no expressive power to
CSS and offers no accessibility benefits.

> As far as I can tell from various websites I see
> around, it seems to be getting primarily used by people who
> resisted switching from pixel dimensions to relative at all, as a
> more comfortable way of switching.

That's possible. Using rem is like using em, just simpler from a naive
perspective and with essentially limited browser support. Authors who
work with pages containing font-size settings on nested elements may get
confused - say, if you have body { font-size: 16px } (yes, those people
often set the basic font size in pixels, defeating the very idea of em
rather effectively) and a div inside with font-size: 90% and then inside
that div another div with font-size: 80%, and then they want to set
something in terms of "body em". They would need to do some calculations...

I don't see any point in using rem if you wish to cover all major
browsers, since you would still need to use em valued settings as backup
- so why not simply use em?

Yucca

From: deborah.kaplan@suberic.net
Date: Thu, May 30 2013 10:45AM
Subject: Re: EM vs. REM?
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On Thu, 30 May 2013, Jukka K. Korpela wrote:
> There isn't much to talk about it, since it adds no expressive power to
> CSS and offers no accessibility benefits.

Thanks! That's what it looked like to me but I wanted to confirm.

Deborah Kaplan
Accessibility Team Co-Lead
Dreamwidth Studios LLC

From: Nancy Johnson
Date: Thu, May 30 2013 11:35AM
Subject: Re: EM vs. REM?
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I ditto Jukka... maybe I'll look at it after IE9 goes away...however
I like percentages and ems...

Nancy Johnson

On Thu, May 30, 2013 at 12:45 PM, < = EMAIL ADDRESS REMOVED = > wrote:
> On Thu, 30 May 2013, Jukka K. Korpela wrote:
>> There isn't much to talk about it, since it adds no expressive power to
>> CSS and offers no accessibility benefits.
>
> Thanks! That's what it looked like to me but I wanted to confirm.
>
> Deborah Kaplan
> Accessibility Team Co-Lead
> Dreamwidth Studios LLC
> > >