This is a placeholder for a namespace document that permits dereferencing the Timed Text Markup Language (TTML) 1.0 namespace URIs:

http://www.w3.org/ns/ttml
http://www.w3.org/ns/ttml#parameter
http://www.w3.org/ns/ttml#parameter-extension
http://www.w3.org/ns/ttml#styling
http://www.w3.org/ns/ttml#styling-extension
http://www.w3.org/ns/ttml#metadata
http://www.w3.org/ns/ttml#metadata-extension

This namespace is stable!