Remove #textOrientation-sideways-LR.

[skynavga]

The semantics of sidewaysLeft, specifically, a 90 degree counter-clockwise rotation, is not well defined in the context of vertical, top-to-bottom inline progression line layout. For example, rotating latin text 90 degrees counter-clockwise would effectively make it a bottom-to-top inline progression layout, which is not supported by any (currently) defined writing mode in TTML. Reviewing both UTR50 and CSS Writing Modes Level 3 reveals that in all cases, only 90 degree clockwise rotation is sanctioned.

Since we have marked #textOrientation-sideways-LR as at-risk, I suggest we remove this feature, including the semantics of sidewaysLeft which appears to sanction a less than well-defined CCW rotation.

Although this is a substantive change, it is permitted prior to PR without triggering a new CR since it has been marked at risk.

[nigelmegitt]

only 90 degree clockwise rotation is sanctioned.

@skynavga I'm trying to understand why sideways is no longer writing mode dependent - are you saying here that UTR50 and CSS writing mode level 3 do not set a writing mode dependency on the rotation angle?

[skynavga]

@nigelmegitt correct; as I said yesterday, neither UTR50 nor CSS WM3 define any use of CCW rotation, so it all uses of sideways map to 90CW