Key scopes and topicsetref

[Eliot Kimber <ekimber@contrext.com>]

In the case of topicsetref and topicset, the 1.3 did not add any language
to define what the behavior should be when either or both of the
topicsetref and topicset specify a value for @keyscope.

There are four possible cases:

1. No key scopes. This is the 1.2 case and nothing is changed
2. Key scope on topicsetref but not on topicset
3. Key scope on topicset but not on topicsetref
4. Key scope on both topicsetref and topicset

In cases (2) and (3) I think the correct behavior can only be that there
is one effective scope reflecting the scope name specified. While
topicsetref is defined as a use-by-reference of the topicset I don't think
just throwing away a keyscope specified on it would ever be
appropriate--it's not a literal replacement but an application-managed
relationship between the navigation point in the referencing map and the
navigation structure defined by the topicset and that definitely argues
for maintaining the keyscope.

In case (4) there are four possible behaviors:

1. The two scope names are merged as for map-to-map references, resulting
in one key scope with two names.
2. The topicsetref's scope becomes the parent scope of the topicset's key
scope
3. The topicsetref's key scope is ignored
4. The topicset's key scope is ignored

Option (1) is consistent with the explicit rules for map-to-map references
and is my preference since it has the least surprise.

Option (2) is logical but surprising and seems inconsistent with the
semantic of topicsetref as a use-by-reference.

Options (3) and (4) are conref-type behaviors and in a real conref would
be controllable via the -use-conref-target keyword in the attribute value.
That option is not available here so I think we can discard these options,
especially since the writeup of topicsetref explicitly says it's not a
content reference.

I don't recall ever discussing the implications of key scopes for
topicsetref. Did we?

Based on my informal survey on DITA Users it doesn't appear that anyone
much uses topicsetref.

But probably good for us to decide what the right answer is or explicitly
defer a decision to DITA 2.0.



----
Eliot Kimber, Owner
Contrext, LLC
http://contrext.com