mbeckerle commented on issue #243: Fixed choice with dispatch key on array 
element.
URL: 
https://github.com/apache/incubator-daffodil/pull/243#issuecomment-504435145
 
 
   The idea is to insure invariants the software depends on are being upheld. 
This particular invariant is that any sequence, even just the one implied when 
a choice has an array element child, can be asked for its format annotation 
object, and one is positively returned, even if it's an empty one containing no 
annotations. 
   
   The separators of an enclosing sequence do not appear around array element 
occurrences for a choice branch that is an array element. To achieve that you 
need an explicit sequence surrounding the array element so you can express the 
separator. 
   
   The rationale here is that choices don't get to express separator 
properties, but that's where they would have to appear if the choice branch 
(that is an array element) was to have separators. 
   
   I suppose the alternative would be to say choices are transparent to 
separation by an enclosing sequence. But that's not true if the choice 
expresses initiator/terminator, which choices are allowed to have.  I lost this 
battle long ago in the DFDL Workgroup. My position was only sequences should 
have delimiters of any kind, period, but this did not win the day, as other 
existing format description systems including some based on XSD, allowed these 
sorts of properties to be expressed on a variety of constructs. 

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