Applying direction to a whole document.

[r12a]

This is a comment from the i18n WG, however we recognise that it comes late in the process for 2nd Edition, so we recommend that if it is not fixable before your transition, you consider it when you start work on the 3rd Edition.

10.2.12 tts:direction
https://w3c.github.io/ttml2/index.html#style-attribute-direction

tts:direction only applies to p & span. Is it possible/useful to specify the base direction at a higher level (e.g. for the tt element)? This would save time for content authors, especially those dealing with RTL scripts. Does the writing-mode attribute address this?

[skynavga]

The commenter may be confusing the notion of a property applying to an element and the notion of where a property is specified (as an XML attribute). Every TTML style property may be specified on any element that permits TTML style properties. For example, the tts:direction attribute may be specified on region, div, p, span and initial elements, etc., but may not be specified on the root tt element. As a style property, tts:direction is inherited. Furthermore, its initial value may be overridden by specifying it via the initial element. Finally, it possesses special semantics related that are documented in [1].

If an author wishes to specify a direction that applies to the entire document, then it would depend on whether only one writing mode is being used or not: if that writing mode is rltb, then I would use the following technique:

<initial tts:writingMode='rltb`/>

This would cause all regions to use the right-to-left, top-to-bottom writing mode, which would then select the rtl direction as the computed value of tts:direction on each region according to the special semantics [1].

[1] https://www.w3.org/TR/2018/REC-ttml2-20181108/#style-attribute-direction-special-semantics