ISSUE-419: Overflow recommendations + #overflow feature

Overflow recommendations + #overflow feature

Raised by:
Glenn Adams
Opened on:
The following statement (section 6.4) is problematic if the document specifies

<ttp:feature value='required'>#overflow</ttp:feature>

"A Document Instance should be authored assuming strict clipping of content that falls out of region areas, regardless of the computed value of tts:overflow for the region."

The reason being that if a document requires support for #overflow, then the presentation processor must support the semantics of both 'hidden' and 'visible' values. Therefore, if this same document includes:

<region tts:overflow='visible'/>

then the author can assume that content that falls outside the region but remains within the root container region is visible and not clipped. On the other hand, content that falls outside the region and the root container region may (or may not) be clipped.
Related Actions Items:
No related actions
Related emails:
  1. {minutes} TTWG Meeting 2015-10-15 (from on 2015-10-15)
  2. {agenda} TTWG Meeting 2015-10-15 (from on 2015-10-14)
  3. RE: {agenda} TTWG Meeting 2015-10-08 (from on 2015-10-08)
  4. {agenda} TTWG Meeting 2015-10-08 (from on 2015-10-07)
  5. {agenda} TTWG Meeting 2015-10-01 (from on 2015-10-01)
  6. {agenda} TTWG Meeting 2015-09-24 (from on 2015-09-23)
  7. Update re: outstanding IMSC1 issues (from on 2015-09-21)
  8. ISSUE-419: Overflow recommendations + #overflow feature [TTML IMSC 1.0] (from on 2015-09-21)

Related notes:

As I recall, the note in Section 6.4 was added to warn authors that, even if tts:overflow='visible' and #overflow is supported, there is no guarantee that text will be displayed, e.g. it can overlap with another region, run past the edge of the root container, etc...

In other words, the idea is that authors should really author their documents so that overflow does not happen.

Pierre-Anthony Lemieux, 21 Sep 2015, 17:28:38

Note also the text from TTML1 §8.2.15 tts:overflow :

> If the value of this attribute is visible, then content should not be clipped outside of the affected region, and region composition and layout must be performed as if the region's width and height were unconstrained, but with a well-defined origin. If the value is hidden, then content should be clipped outside of the affected region.

I recall that the text referenced in this issue was added to address the fact that the TTML1 spec only has SHOULDs so conformant presentation processors can ignore the tts:overflow attribute value.

Nigel Megitt, 22 Sep 2015, 15:02:06

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