imsc1/spec/imsc-extension-namespace.html

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    <title>TTML Text and Image Profiles for Internet Media Subtitles and Captions 1.0 :: Extension Namespace</title>
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<p>This namespace is specified at <a href="http://www.w3.org/TR/ttml-imsc1/">TTML Text and Image Profiles for Internet Media Subtitles and Captions 1.0</a></p>

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