#396: "Suggesting file path display base to viewers": Revised proposal

After Jim presented this proposal, there was a lot of follow-on discussion with Jim, Michael, and me. All agreed that it  is valuable to provide this hint to viewers; the discussion was about how to represent it:
As a reserved property name   DISPLAYBASE   in   run.originalUriBaseIds  .
As a property name   SARIF_DISPLAYBASE   in a reserved   SARIF_  -prefixed  "namespace" in   run.originalUriBaseIds  .
As a new property   run.displayBase  .
All of these had drawbacks:
#1 requires a reserved name, and requires that name to be treated specially (not actually  used  as a   uriBaseId   value  anywhere else in the log file). Also, it implies that if we added any other "special" values in the future, it would be a breaking change, since an implementer might have already used whatever value we chose.
#2 also requires a reserved name that can't actually be used as a   uriBaseId   elsewhere  in the log file. It has the advantage over #1 of allowing additional special values to be defined in a non-breaking way, at the cost of defining a mini-language on the property names.
#3 doesn't have the drawbacks of #1 or #2, but if we define other special URIs in future, we'd have a proliferation of properties on the   run   object.
@michaelcfanning
 and I propose  this alternative:
Define a property   run.specialLocations   with a single property   displayBase   whose  value is an   artifactLocation  . In future, additional specially treated locations can be defined in a non-breaking way by defining new properties  on   run.specialLocations  .
It has these advantages:
It doesn't require a reserved and specially treated   uriBaseId   value.
It doesn't require a namespace on   uriBaseId   values.
It allows new "special" locations to be defined in a non-breaking way.
It avoids a proliferation of properties on the   run   object.
It has this disadvantage:
It requires a schema change to define the new object.
@michaelcfanning
 and I  are willing to take the pain of the schema change to get the other benefits.

Thanks,
Larry