ISSUE-215: Negative extent lengths should be prohibited.

negative extent

Negative extent lengths should be prohibited.

State:
CLOSED
Product:
TTML 1.0
Raised by:
Glenn Adams
Opened on:
2013-05-26
Description:
After further research, I believe the language I added to TTML10SE 8.2.7 [1] is misleading:

"where, if either width or height is negative or zero, then extent must be considered zero in both inline and block progression dimensions."

[1] https://dvcs.w3.org/hg/ttml/raw-file/default/ttml10/spec/ttaf1-dfxp.html#style-attribute-extent

Looking further into both XSL-FO and CSS2, one finds explicit statements:

"Negative values for 'height' are illegal." [2][3]
"Negative values for 'width' are illegal." [4][5]

[2] http://www.w3.org/TR/2006/REC-xsl11-20061205/#height
[3] http://www.w3.org/TR/2008/REC-CSS2-20080411/visudet.html#propdef-height
[4] http://www.w3.org/TR/2006/REC-xsl11-20061205/#width
[5] http://www.w3.org/TR/2008/REC-CSS2-20080411/visudet.html#propdef-width

Since we defined tts:extent as a derivation of XSL-FO height/width [6], these prohibitions already effectively apply. However, to ward off mis-interpretations by readers, I suggest we add similar language proscribing negative extent lengths to make this clear. Note that no change will be made to the XSD, since we use xs:string as the data type, which means this is a semantic validity rule that applies to the PSVI.

[6] https://dvcs.w3.org/hg/ttml/raw-file/default/ttml10/spec/ttaf1-dfxp.html#attribute-vocab-derivation-table

Related Actions Items:
No related actions
Related emails:
  1. Minutes - 2013-06-27 (from glenn@skynav.com on 2013-07-11)
  2. RE: TTML Agenda for 26/06/13 (from mdolan@newtbt.com on 2013-06-27)
  3. TTML Agenda for 26/06/13 (from Sean.Hayes@microsoft.com on 2013-06-27)
  4. Re: TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from tai@irt.de on 2013-06-19)
  5. TTML Agenda for 20/06/13 -- update -- (from Sean.Hayes@microsoft.com on 2013-06-19)
  6. Re: TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from glenn@skynav.com on 2013-06-19)
  7. Re: TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from tai@irt.de on 2013-06-19)
  8. Re: TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from glenn@skynav.com on 2013-06-18)
  9. Re: TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from glenn@skynav.com on 2013-06-18)
  10. TTML Agenda for 20/06/13 -- ADVANCE NOTICE -- (from Sean.Hayes@microsoft.com on 2013-06-17)
  11. TTML Agenda for 30/05/13 (from Sean.Hayes@microsoft.com on 2013-05-29)
  12. ISSUE-215 (negative extent): Negative extent lengths should be prohibited. [TTML 1.0] (from sysbot+tracker@w3.org on 2013-05-26)

Related notes:

Fixed in https://dvcs.w3.org/hg/ttml/rev/60bbc0feed94

Glenn Adams, 26 May 2013, 19:28:26

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David Singer <singer@apple.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, Chairs, Thierry Michel <tmichel@w3.org>, Philippe Le H├ęgaret <plh@w3.org>, Staff Contacts
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