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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/commits/imsc-cr3 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 CR (20150519) to CR (20160126)
===================================

* ISSUE #63: Liberation open source font added to reference fonts (Appendix A) 

* ISSUES #68, #69 and #103: performance of the HRM altered for scripts where mapping 
  of characters to glyphs is generally not one-to-one, and clarified that overflowing
  the Glyph Buffer is an error (Section 9.5)
  
* ISSUE #49: requires content processor to implement #lineBreak-uax14
  
* ISSUE #41: clarified constraints on ittp:aspectRatio parameters

* ISSUES #85, #50, #53, #54, #57, #77, #78, #85 and #112: clarified conformance
  requirements for content processors and documents conforming to each profile,
  and made explicit dependencies between related features

* ISSUE #94: clarified that empty div elements with smpte:backgroundImage attribute generate ISDs

* ISSUE #96: definition of "Presented Image" modified

* ISSUE #97: clarified smpte:backgroundImage processing requirements

* ISSUE #61: replaced "earlier" with "lexically precedes" in Section 6.7.2

* ISSUE #84: clarified that the mapping algorithm of Section 6.7.1 applies to each 
  image frame of the Related Video Object
  
* ISSUE #101: clarified that only "px" could be used when specifying tts:extent in Image profile

* ISSUE #118: clarified that, in Image profile, only one div element can be present
  in a presented region in a given ISD


From CR (20141209) to CR (20150519)
===================================

* ISSUE-364: when expressed in pixels, the extents of the root container
  is no longer required to be equal to the dimensions of the related video object frame

* ISSUE-367: adopted initial values for @tts:displayAlign and @tts:textAlign
  as defined in TTML 1SE

* ISSUE-375: clarified constraints on @ebutts:linePadding and
  @ebutts:multiRowAlign position per EBU-TT-D normative reference

* ISSUE-377: adopted rounding rules as defined in TTML 1SE

* ISSUE-378: the product of @ttp:frameRate and @ttp:frameRateMultiplier is no longer
  required to be equal to the frame rate of the related video object

* ISSUE-382: recommended practice added for the use of @begin and @end attributes
  on content elements

* ISSUE-388: the presence of @ttp:timeBase is no longer required

From WD (20140330) to CR (20141209)
===================================

* #length-cell constraint does not apply to ebutts:linePadding (Section 6.10)

* Clarified that ittm:altText is intended to be a child of a metadata element (Section 6.7.4)

* Clarified that the namespaces defined by this specification are mutable and that
  all undefined names in these namespaces are reserved for future standardization by the W3C
  (Section 6.3)