Re: [css-device-adapt] MSFT feedback on latest editor's draft

On Mon, Dec 9, 2013 at 9:49 PM, Matt Rakow <> wrote:
> Hi all,
> I've been getting caught up recently on the edits made to the Device Adaptation ED and wanted to provide some feedback.
> 1. Explicit values for initial viewport width and height
> In the latest ED the named values of "device-width" and "device-height" have been removed, and instead declaring a width or height of "auto" is intended to provide equivalent behavior.  However, "auto" is already the default value, indicating that the UA's default behavior may apply - the behavior just changes if you explicitly set the width or height to "auto".

'auto' width means the value will be deduced from the height (using
aspect ratio of the initial viewport) and vice versa. 'auto' will be
resolved to initial viewport width/height if all min/max-width/height
are 'auto'. The difference between 100% and 'auto' is that 100% will
not be affected by the length in the other direction.

  @viewport { min-width: 200%; height: auto; } /* height resolves to
200% of initial viewport height */
  @viewport { min-width: 200%; height: 100%; } /* height resolves to
initial viewport height. */

There is no difference between an initial 'auto' value and an explicit
'auto' value. 'auto' should not reflect the default behavior of the
browser if the browser sets a default width that is different from the
initial viewport width. That should be expressed as an @viewport rule
in the UA stylesheet instead. For instance:

  @viewport { min-width: 1024px; }

> IE uses "auto" to reflect the default behavior of the browser (i.e. actual viewport is minimum 1024px by default), whereas "device-width" and "device-height" map to the dimensions of the initial viewport (matching the current WD).  I'd like to add the named values back so we can keep these concepts distinct, and so that "auto" only has a single meaning.

As mentioned above, 'auto' should not have different meanings, and a
default width different from the initial viewport width should be
expressed in the UA stylesheet.

> I agree that device-width/device-height are probably not the right vocabulary to use though.  Perhaps a renaming would be appropriate ("initial-viewport-width"?  "window-width"?  "css-pixel-width"?).

Initial viewport width/height can be expressed as 100vw or 100vh.
Since vw/vh are valid units for <length> in CSS Values and Units we
shouldn't need an additional keyword.

> 2. min- and max- width and height
> Currently, there are two ways to provide a viewport "range."  These are the min- and max- prefixes for the width and height properties, and the interaction of @viewport with width and height media queries.  Having both of these mechanisms adds a pretty significant amount of complexity to the ways this feature can be applied, especially if both are used simultaneously.
> I'd argue that the min- and max- prefixes for the width and height properties are not necessary for the scenarios developers are interested in, and that equivalent functionality can be built using only media queries for range constraints.  For example, consider the two following rules:
> /* Example A */
> @viewport {
>     min-width: 640px;
>     max-width: 960px;
> }
> /* Example B */
> @media (min-width: 640px) and (max-width: 960px) {
>     @viewport { width: device-width; }
> }
> Both of these rules suggest the author has done the work necessary to ensure their site works well for widths between 640 and 960px, and both are equivalent for initial viewports within that range.  However, outside of that range the behavior differs.  The primary difference is that Example A forces scaling for all window sizes outside of the designed-for range, while Example B leaves the UA in charge of what happens to those sizes.  I see Example B as the better option, as the potentially unbounded scaling of Example A will likely end up with an unintended result for extreme viewport sizes.  Consider the ~200% scaling that would occur on a 1080p monitor, for example.
> I'd be interested in removing the min/max option from the spec, if there is not a particular scenario they are required for.

In Example B, you will get an actual viewport of 1024px for initial
viewports < 640px when you have a UA default of 1024px. So you would
probably want to add an @viewport rule for the widths < 640px too.

The original spec proposal didn't have min/max values. Fantasai wanted
min/max values and, IIRC. The use case was to express that you made a
site that could adapt to viewports above a certain size but cap to a
minimum-width. For instance: @viewport { width: 640px auto; }

Without min/max support I see that you can express that as:

  @viewport { width: auto; }
  @media (max-width: 640px) {
    @viewport { width: 640px }

Rune Lillesveen

Received on Tuesday, 10 December 2013 08:16:35 UTC