Another proposal for 'shared' ta parts

[Stephen Green <stephen.green@documentengineeringservices.com>]

Here's what I've found I can define in the schema, in line with
Jacques' original
proposal, I think:

1. Scrap 'overrides'
2. Scrap 'compositions'

3. 'shared' contains all of the TA parts

4. all except 'prerequisite', 'predicate' and 'prescription' simply
obey a default
(for most they compose, and 'var' is a declaration with TA Set scope)

5. 'prerequisite', 'predicate' and 'prescription' have a 'conflict' attribute
     with controlled code values

6. the values are any or all of the following
'overriding'||'overridden'||'conjunction'
     ||'disjunction'  but 'prescription' might allow one subset of these wheras
     'predicate' might allow all of these, say

7. the values can be extended (if you put 'ext:...' as a prefix to the
extension value)
    and an implementation is allowed to ignore the extensions which it doesn't
    'understand'

Example (perhaps not a good one)

<testAssertionSet>
...
<shared>
...
        <target>widget</target>
...
        <prerequisite conflict="overriding" lg="en-us">has a button on
top</prerequisite>
        <predicate conflict="disjunction" lg="en-us">has a red button
on top</predicate>
        <prescription conflict="overridden"
level="optional">overridden by mandatory TAs in set</prescription>
...
</shared>
...
<testAssertion>
...
</testAssertion>
...
</testAssertionSet>

8. predicates presumably need all four values; prerequisites just
'conjunction' and
    'disjunction' and prescriptions just 'overridden' and 'overriding'

9. some future implementers might want to have prescription which can
    'override' the existing level with an extended 'ext:deprecated' level, say
    using the old TA in a TA Set with this deprecating 'prescription'
in 'shared'

Best regards
---
Stephen D Green