[Change] XML Schema and XSLT Stylesheet [Bugzilla] lack of syntactic symmetry between the control flow expressions [Category] Substantive. [Description] 
Eliminated the possibility of defining three "error variables" as part of the catch clause; those variables (and others) are now implicitly defined, and may be used without explicit definition. At the same time, fixed a bug in the schema and stylesheet that recognized and produced invalid syntax for the validation expression.