Can I create an XSD schema that places an attribute on all complex types?

Question

I would like to create an XSD that defines an attribute which can be placed on elements from other schemas, or elements that are not in any schema. For example, the schema

Answer 1

Consider xsi:nil, xsi:schemaLocation and xsi:noNamespaceSchemaLocation. The answer is yes.

It also wouldn't have taken long to try it out and see.

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You were missing a targetNamespace in the schema. Try this: