IMSC1 Comments - More #12 - HRM

   - Section 9.3 PAINT() refers to a SIZE() function which appears to be
   defined later with the name NSIZE().


   - Section 9.4 refers to IDec in the text but Idec in the parameter table.


   - Section 9.5 uses the phrases "Normalized Glyph Buffer Size" and "Glyph
   Buffer Normalized Size"; these should be made consistent.


   - The definition of identical glyph use in section 9.5 is not adequate
   in the general case in which glyph mapping process is context sensitive.
   For example 'f' and 'i' may map to a ligature glyph for font F0 but to
   distinct glyphs for font F1. Similarly, for Arabic text and other complex
   scripts, the glyph mapping process is based on the font's GSUB tables and
   the set of active features and language bindings.


   - The statement "Gr and Gc shall include only glyphs in presented regions
   <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html#dfn-presented-region>
    and shall not include a [UNICODE
   <https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html#bib-UNICODE>]
   Code Point if it does not result in a change to presentation, e.g. the
   Code Point is ignored." is rather unusual in that it erroneously refers
   to glyphs in terms of a Unicode Code Point. Glyphs and glyphs codes are not
   directly related to Unicode code points. It would be better to say that a
   glyph that does not contain any renderable outline is ignored. But that is
   rather redundant since font designers do not include glyphs in fonts that
   do not have a renderable outline.


   - Is it correct to say that the only independent variables in the HRM
   are as follows?


   - extent of root region
      - number and extent of non-root regions
      - number and extent of images in image profile (which should match
      1:1 the number and extent of non-root regions in a given ISD)
      - number and (vertical) font size of glyphs in regions in text
      profile, and whether each glyph is a CJK ideograph or not


   - Needs description (and possibly an example) of a document (for each
   profile) that would result in an HRM error given the default parameter
   values.


   - Does the HRM capture the composited painting requirements for the
   multiple layers of background colors? i.e., region, body, div, p, and span
   can all have distinct background colors that must be composited. I ask this
   because 9.2 steps 2 and 3 seem to imply only two potential background color
   layers, and not 5 layers as is permitted. The reason they may need to be
   composited is because each of these 5 layers may specify an alpha component
   in their color specification. In addition, tts:opacity applies to a
   region's content as a whole, and tts:color for text foreground can also
   specify alpha. Overall, that yields 7 possible compositing steps to a
   presentation buffer (in text profile).