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RE: New Features and CSS Compatibility

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Tue, 5 Nov 2013 11:45:14 +0000
To: John Birch <John.Birch@screensystems.tv>, Glenn Adams <glenn@skynav.com>, TTWG <public-tt@w3.org>
Message-ID: <E9A92BD0A4FC934EB7935470A46D1524245E18AA@DB3EX14MBXC324.europe.corp.microsoft.com>
CSS does in fact have a shrink-to-fit concept http://www.w3.org/TR/CSS21/visudet.html#shrink-to-fit-float:

10.3.5 Floating, non-replaced elements
If 'margin-left'<http://www.w3.org/TR/CSS21/box.html#propdef-margin-left>, or 'margin-right'<http://www.w3.org/TR/CSS21/box.html#propdef-margin-right> are computed as 'auto', their used value is '0'.
If 'width'<http://www.w3.org/TR/CSS21/visudet.html#propdef-width> is computed as 'auto', the used value is the "shrink-to-fit" width.
Calculation of the shrink-to-fit width is similar to calculating the width of a table cell using the automatic table layout algorithm. Roughly: calculate the preferred width by formatting the content without breaking lines other than where explicit line breaks occur, and also calculate the preferred minimum width, e.g., by trying all possible line breaks. CSS 2.1 does not define the exact algorithm. Thirdly, find the available width: in this case, this is the width of the containing block minus the used values of 'margin-left', 'border-left-width', 'padding-left', 'padding-right', 'border-right-width', 'margin-right', and the widths of any relevant scroll bars.
Then the shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).

And so there is *a* mapping, if not ideal, as these pages demonstrate:


However it may require some amount of creativity to apply to the TTML mapping.
I believe the CSS WG have attempted to reuse this concept elsewhere in CSS3.
From: John Birch [mailto:John.Birch@screensystems.tv]
Sent: Tuesday, November 5, 2013 10:29 AM
To: Glenn Adams; TTWG
Subject: RE: New Features and CSS Compatibility

Hi Glenn,

Yes, I would agree… except that I have no exposure to CSS or to the process involved in changing / extending it.

My proposal is simply meant as a statement of desired functionality… I defer to those with better understanding of the supporting technologies to consider how it might be implemented. I accept that it is likely ☹ that the (correct IMHO) choice by TTWG of CSS / XSL:FO as referenced standards may mean that my ‘shrink to fit’ desires are not possible. This being simply because those underlying frameworks were not constructed ‘with a mindset’ that would support such behaviour. None- the-less, I stand by my proposal for consideration at TPAC, since it might be the case that my ‘use case’ has not been considered, and it might be the case that individuals attending can see a route to a solution… even if such a solution may be a long time coming and require a new version of CSS / XSL:FO (or require that TTML reference a different, equivalent but more flexible rendering framework). I note with interest that CSS3 includes flex-box layout functionality – cursory inspection would suggest this might be relevant.

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From: Glenn Adams [mailto:glenn@skynav.com]
Sent: 05 November 2013 01:10
Subject: New Features and CSS Compatibility

For anyone suggesting a new feature in TTML, e.g., shrink text to fit region, it won't be of much benefit to do so if there isn't an existing CSS mapping, or at least not much benefit in the open web platform (native presentation processors can do what they want).

So before you consider proposing something that has no CSS mapping, think first about how to get it into CSS.

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Received on Tuesday, 5 November 2013 11:46:26 UTC

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