The #extent feature implies #extent-auto.

[palemieux]

Since auto was defined in TTML1 as part of the tts:extent attribute

[skynavga]

No change is required, since by transitive closure with support for #extent-{region,root}, we already have support for #extent-auto (and #extent-length), as well as a proscription against their prohibition.

[nigelmegitt]

I follow that logic @skynavga but I think the request was to include #extent-auto in the note about implied related feature support under #extent, which would not be false, and may be useful. @palemieux is that something you still want to add?

[skynavga]

@nigelmegitt I don't want to do that because that would mean I need to add all implications and proscriptions to other feature definitions that involve transitive closures. That is a bad specification strategy and subject to errors from saying the same thing twice (or more).