Re: [css-device-adapt] How should initial viewport contribute to layout?

Let me explain more about how my questions are related to the spec :)

- Many browsers attach fixed-pos elements to the initial viewport (or sth
between the initial viewport and actual viewport) instead of the actual
viewport. Perhaps we could say they are wrong because they don't follow
existing specs, but perhaps we'd better look into the reasons of their not
following spec, and maybe adjust the spec if the reasons are reasonable.

- In my understanding of the spec, initial viewport is visual viewport. The
spec says the actual viewport should be proportional to the initial
viewport if viewport height is 'auto' or ..., so if my understanding were
correct, not adjusting actual viewport on initial viewport change (even if
it's temporary) would not be following the spec. The question is about: 1.
if the understanding is correct; 2. whether the browsers are wrong or the
spec needs to be adjusted.


On Tue, Feb 11, 2014 at 5:39 PM, Xianzhu Wang <>wrote:

>> All this said, I'm not sure if these questions fall into the device
>> adaptation spec since they pertain more to definition of visual viewport
>> vs. actual viewport, rather than the definition of initial viewport vs.
>> actual viewport.  I do think they'd be good questions to resolve in some
>> spec though.
> I think this is a good point. Do you mean we should distinguish 'visual
> viewport' and 'initial viewport'?
> Thanks,
>> -Matt
>> >From: [] On Behalf
>> Of Xianzhu Wang
>> >Sent: Tuesday, February 11, 2014 11:42 AM
>> >To:
>> >Subject: [css-device-adapt] How should initial viewport contribute to
>> layout?
>> >
>> >Hi,
>> >
>> >Actually I have 2 related questions:
>> >1. Should fixed-position blocks layout according to the 'initial
>> viewport', 'actual viewport' or something between them?
>> >2. For a page with unconstrained viewport height, how should the height
>> of the 'actual viewport' be adjusted when there is temporary height change
>> of the 'initial viewport', e.g. when the on-screen-keyboard shows?
>> >
>> >The answers to the above questions seem to have already been covered by
>> existing specs, but after we examine the current behavior of different
>> mobile browsers we found they have tweaked the existing specs to achieve
>> more user-friendship and/or better performance:
>> >
>> >1. All browsers seems not to layout top-level fixed-position blocks
>> according to the initial-containing-block (i.e. 'actual viewport' in
>> css-device-adapt), but somehow according to the visible viewport (i.e.
>> 'initial >viewport' in css-device-adapt). Mobile Safari's behavior is more
>> complex that seems to use a bigger virtual viewport to contain the
>> fixed-position elements if the visible viewport is too small.
>> >
>> >2. For a page with unconstrained viewport height, the browsers behave
>> differently about whether to adjust the actual viewport height when
>> visibility of the top- and/or bottom- controls and the on-screen keyboard
>> changes.
>> >
>> >
>> the current behaviors of the browsers.
>> >
>> >I think it'd be better if the spec address the issues that caused the
>> browsers to tweak the spec, to avoid inconsistency and confusion.
>> >
>> >Thanks,
>> >Xianzhu
>> >

Received on Wednesday, 12 February 2014 19:23:55 UTC