ACTION-318: Draft note wording for imsc conformance

As discussed yesterday, I propose the following wording for a non-normative note to be added to section 3. Conformance of IMSC:

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NOTE
The terms Presentation Processor and Transformation Processor are defined by [TTML1] in general terms and more specifically with requirements for conformance with reference to the DFXP Presentation Profile and Transformation Profile. The use of those terms in this document does not imply that conformance to both the profiles defined herein and the relevant DFXP profile is required. It is not considered an error for a processor to be a conformant presentation processor or transformation processor in the context of this document without being a conformant TTML presentation processor or transformation processor.
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Kind regards,

Nigel