[Bug 5063] Inheritance of some SML reference constraints

http://www.w3.org/Bugs/Public/show_bug.cgi?id=5063

           Summary: Inheritance of some SML reference constraints
           Product: SML
           Version: FPWD
          Platform: PC
        OS/Version: Windows XP
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Core
        AssignedTo: cmsmcq@w3.org
        ReportedBy: sandygao@ca.ibm.com
         QAContact: public-sml@w3.org
 BugsThisDependsOn: 4643


(Bug 4643 is one instance of such inheritance.)

This involves sml:target* and SML identity constraints.

These constraints are inherited in 2 cases:
1 If they are specified on a global element declaration G then they are
inherited by other element declarations in G's substitution group
2 If they are specified on an element declaration E that appears in a complex
type definition B, then they are inherited by E's corresponding element
declarations in types derived by restriction from B.

For #1, XML Schema only inherits type definitions from substitution heads, but
not for things like block, final, default, fixed, nillable, etc. For #2, XML
Schema doesn't specify any inheritance rule. Elements in the restriction type
must specify what they need.

We need to answer the same set of questions raised in bug 4643.