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* Summary of substantive changes *
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NOTE 1: This summary is provided for illustration only. For an exhaustive list of changes, please
refer to the changesets at https://github.com/w3c/imsc or use the W3C diff tool at
http://services.w3.org/htmldiff across published versions of the specification.

NOTE 2: Issues and their dispositions are documented at https://github.com/w3c/imsc/issues


From WD (20171017)
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* Clarify the use of recommended character sets (#236)

* Update feature list per TTML2 CR (#341)

* Refactor profile signaling provisions (#331)

* Remove recommendation against TAB characters per TTML2 semantics (#353)

* Clarify fillLineGap semantics when applied to successive <p> elements (#263)

* Clarify forcedDisplay semantics (#284)

* Clarify handling of foreign elements and attributes (#213)

* Clarify style resolution procedure (#300)

* Remove recommendations on time expressions and ttp:cellResolution (#329)

* Remove ttp:version and fix examples (#261)

* Prohibit simultaneous tts:origin and tts:position (#289)

* Remove background-color feature per removal in TTML2 (#255)

* Remove rubyOverhang related features (#286 and #285)

* Deprecate ittp:aspectRatio in favor of ttp:displayAspectRatio (#273)

* Deprecate ittm:altText in favor of altText named metadata item (#274)

* Deprecate #progressivelyDecodable (#272) 

* Deprecates #writingMode-horizontal-rl in Image Profile (#147)

* Updated profile signaling and resolution to match TTML2 semantics (#3, #124 and #125)