Remove #textOrientation-sideways-LR and related semantics (#980).

[skynavga]

Closes #980.

[css-meeting-bot]

The Timed Text Working Group just discussed Remove #textOrientation-sideways-LR and related semantics (#980). ttml2#981, and agreed to the following:

• SUMMARY: Pull request review to continue.

The full IRC log of that discussion

<nigel> Topic: Remove #textOrientation-sideways-LR and related semantics (#980). ttml2#981
<nigel> github: https://github.com//pull/981
<nigel> Glenn: Summary here is that sideways-left is not well defined and problematic because
<nigel> .. in our top to bottom inline progression direction vertical writing directions, if you turn
<nigel> .. English text on the side to the left, then the first letter of the sentence appears at the
<nigel> .. bottom of the screen and proceeds from bottom to top. The alternative is to do them
<nigel> .. top to bottom and have a partial mirror image of the text vertically, which would be
<nigel> .. hard to read. When I reviewed CSS writing modes level 3 and UTR50 the conclusion I
<nigel> .. reached is that sideways-left is not well defined. I could implement it but it wouldn't
<nigel> .. make any sense and it would be a waste of effort. If I implemented it so it starts at the
<nigel> .. bottom and goes to the top then it contradicts the writing mode definition, without
<nigel> .. introducing a new bottom to top writing mode. This is marked as at risk so my response
<nigel> .. is to remove this and improve the consistency with CSS. It's substantive because it takes
<nigel> .. out both sideways-left and sideways-right, leaving mixed, upright and sideways, where
<nigel> .. sideways always means clockwise, which matches CSS. If we are going to make this
<nigel> .. substantive change we have to do it under the rubrick of changing or removing an at
<nigel> .. risk feature. I need someone to review it.
<nigel> .. TTPE is not going to implement it so at the end we will end up with a red box in the
<nigel> .. implementation matrix.
<nigel> Nigel: Thank you for raising this, and for inviting @r12a to review it. I'd be interested to
<nigel> .. hear his comments.
<nigel> .. I can't recall how this got in to our spec.
<nigel> Glenn: It was in a previous version of a CSS spec but was removed, probably because it
<nigel> .. doesn't make any sense for top to bottom layout.
<nigel> Pierre: Digital Cinema implementations support left and right rotation, but that does not
<nigel> .. mean it is used. I'm not objecting to the removal, just adding a data point as to why we
<nigel> .. may have ended up with this.
<nigel> Glenn: That's fired a neuron in my mind, so it's probably the case.
<nigel> Nigel: I see Pierre just approved it. We have time to let this pull request run its course in
<nigel> .. terms of review so I suggest we allow that.
<nigel> SUMMARY: Pull request review to continue.

[r12a]

I believe this is in line with the recommendations in https://github.com/w3c/ttml2/issues/277. On that basis, i agree with it.

[nigelmegitt]

Noting this is a change to the definition of sideways, in that it is no longer block progression direction dependent.

[nigelmegitt]

Note for a potential editorial tweak at some point in the future: we define sideways in relation to mixed independently of the keyword sideways even though both have exactly the same definition, rotate 90º clockwise, so potentially we could make them both reference the same definition and define the behaviour in one place rather than two. Very minor point!