We have recently revamped our support for XML schema. This includes bug fixes (array types and optional properties were not catered in some cases, issues with circular references, etc.) and addition of missing features (Union of simple types, redefinition of schema types, etc.).
XML schema is widely used in API description formats like WSDL and WADL and we are always working on improving our parsers for these formats. Revamping of XML schema will ensure that the transformation of these formats will result in a better output than before.