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Re: Negative percentages for ACSS pause properties

From: Liam Quinn <liam@htmlhelp.com>
Date: Wed, 06 Aug 1997 19:22:28 -0400
Message-Id: <>
To: Chris Lilley <Chris.Lilley@sophia.inria.fr>, raman@Adobe.COM, www-style@w3.org

At 05:47 PM 06/08/97 +0200, Chris Lilley wrote:
>On Aug 4,  6:38pm, Liam Quinn wrote:
>>   If a UA is to handle negative pauses of any amount, it must
>> process the entire document before rendering any of it.  While 
specifying -
>> 1000s is silly, UAs will need to be aware of some kind of minimum value 
>> 5s?) to allow rendering while the document is loaded.
>I don't think that requiring buffering is going to add much value. I 
>be glad of arguments for and against.

I guess an argument for is that you could have one portion of a document 
start rendering as the previous portion is finishing, with an overlap that 
could produce some nice effects.  In marking up a play, for example, you 
might have the last part of a narrator's line overlap the first part of an 
explosive speech for a dramatic effect.

An overlap of more than a couple seconds doesn't seem all that reasonable 
to me, but perhaps it's best not to rule it out.  I think this is 
analogous to negative margins in CSS1, where, for margins, a "negative 
value is allowed, but there may be implementation-specific limits." [1]

>> If ACSS allows negative pauses, I think it should give a suggested 
>> that UAs should consider, or (probably better) specify that UAs can
>> arbitrarily set negative pauses to any larger amount up to zero.
>That would make the stylesheets somewhat less interoperable, I suspect.

I can't think of a reason why, off-hand.  Did you have something in mind 

>>  With the
>> latter option, UAs could set their own threshold (perhaps based on the
>> amount of buffering the UA does), and could change extremely small 
>> like -1000s to something more reasonable, like -5s or 0.
>Note that setting buffering to 5s means accepting an additional 5s
>delay between clicking on a link and getting any of the content, compared
>to the situation where negative values are not allowed.

Yes, and for this reason UAs may choose to treat negative values as 0, or 
they may choose their own (or user-configured) threshold.  5s does seem 
like a lot, but 1s?  UAs could treat negative values as 0 unless loading 
files from cache, in which case buffering the entire document (or at least 
large portions of it) would often be unnoticeable to the user.

>There are probably better ways to synchronise different media.

Probably, yes.  There are also better ways to overlap visual elements than 
CSS1's negative margins.  But for quick, simple overlaps, negative margins 
can be much more straightforward than CSS Positioning.

[1] http://www.w3.org/TR/REC-CSS1#margin-top

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Liam Quinn
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Web Design Group            Enhanced Designs, Web Site Development
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Received on Wednesday, 6 August 1997 19:22:13 UTC

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