TTML 1.0 (Editorial)
TTML 1.0 Test Suite
TTML IMSC 1.0
TTML IMSC 2.0
TTML Simple Delivery Profile for Closed Captions (US)
TTML versions and profiles note
TTML WebVTT mapping note
Frans de Jong
Loretta Guarino Reid
Philippe Le Hégaret
The prose in 6.1.3 para 4:
"If the URI expressed by the content of the ttp:feature element is a relative URI, then, when combined with the feature namespace value expressed by the xml:base attribute of the nearest ancestor ttp:features element, it must express an absolute URI. In either case (original absolute URI or resulting absolutized URI), the URI expressed by the ttp:feature element must further adhere to the syntax of a feature designation as defined by D.1 Feature Designations."
requires that the absolutized feature designation adhere to the "feature-designator" syntax in D.1, but does not require its value to have been previously defined in some version of TTML. Since TTML reserves all values for standardization (see D.1, quoted below), we should make clear that the actual values of feature designators must be one of the values defined in TTML 1.0 or some future revision of TTML.
"All values of feature-designation not defined by this specification are reserved for future standardization."
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