Yelp

(The Help System)

ttml.features

The supported features and extensions for TTML documents.

This parameter lists the fully-qualified URIs of TTML features and extensions supported by the stylesheets. The values are in the form of a space-separated list, which MUST have both a leading and a trailing space.

The default value for this parameter is empty. Importing stylesheets should set this to an appropriate value.