Feedback: Rework on index content

["Dr. Stanley Doherty" <stan@modularwriting.com>]

Looks good -- just a few minor questions/comments.
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All page references are to the 7-30-2019 PDF distributed by Kris.

A. Did we lose any 1.3 material in the rework. 
   SDoherty: None that I discern. I like the updated structure.

B. Did it make sense?
   SDoherty: Yes, it read well. Here are some comments and questions. 

   PDF/3 (line 5): Is there a limit on the number of nested <indexterm> 
   levels?

   PDF/3 (line 40-ish): Suggest "determines" instead of "has an effect 
   on".

   PDF/3 (line 48-ish): The first sentence in "Topic prologs or DITA 
   maps" was tough reading - at least for me. Suggest something a bit
   more drawn out: "In a topic <prolog>, <indexterm> is a child of 
   <metadata> and <keywords>. In a map <topicref>, it is the child of
   <topicmeta> and <keywords>."

   PDF/4 (line 4): Suggest "determines" instead of "has an effect 
   on".

   PDF/4 (line 45-ish): Under "Index redirection", would it be more 
   clear to say that redirections only resolve within the scope of 
   <indexterm>s referenced from the root scope?
 
   PDF/6 (line 5): Any restrictions on naming these <indexterm> 
   identifiers?

   PDF/6 (line 5): Can I overload @start or @end with multiple 
   values? <indexterm start="range1 range2">term</indexterm>.
   Multiple ranges may have the same begin or end points.

   PDF/7 (line 40-ish): Suggest some sort of rewording of the 
   paragraph "Now assume . . .." Maybe "Ranges defined in a 
   topic <prolog> cover topics subordinate to that topic in 
   a map branch."

   PDF/10: Noticed that "multilevel" sometimes has a hyphen 
   (multi-level).

   General: What is the expected processing behavior for empty
   <indexterm> elements? Messed up multilevel elements?
   Oxygen deems this valid:
   <indexterm><indexterm>level-2</indexterm></indexterm>
 
   General: Should the @start and @end page references respect
   the bookmap chapter-page pagination references?
 
   General: Precedence question. If I have a shared topic with an
   <indexterm> and I reference that shared topic multiple times 
   within the same map, should processors generate one index entry
   for the first time they read the shared topic? each time they
   ready it?
 

   General: Should we be cross-referencing the bookmap <indexlist/>
   element here? FWIW I get an index by default when I run a 
   map through the PDF2 processor, but need to add <indexlist/> 
   manually to get an index with bookmaps. 

   General: Does <index-base> deserve a mention here? 

   General: Does <index-sort-as> deserve a mention here? 

C. Comments on processing instructions?
   SDoherty: None.