## XSD Schema validation now correctly detects violations of unique constraints if compound keys are used and one key is empty

### Scope
Edge

### Version Introduced
4.6

### Source Analyzer Status
Available

### Change Description

Versions of the .NET Framework prior to 4.6 had a bug that caused XSD validation
to not detect unique constraints on compound keys if one of the keys was empty.
In the .NET Framework 4.6, this issue is corrected. This will result in more
correct validation, but it may also result in some XML not validating which
previously would have.

- [x] Quirked
- [ ] Build-time break

### Recommended Action

If looser .NET Framework 4.0 validation is needed, the validating application
can target version 4.5 (or earlier) of the .NET Framework. When retargeting to
.NET 4.6, however, code review should be done to be sure that duplicate compound
keys (as described in this issue's description) are not expected to validate.

### Affected APIs
* Not detectable via API analysis

### Category
XML, XSLT

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