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Assume that the user adds the element customer to the form's types. All three elements (firstname, lastname and fullname) are required by the type. But, the form designer is not obligated to add all three controls to the form. Let's say the designer adds controls for firstname and lastname but omits fullname. The form will have two invalid controls when initially loaded and the submit button is disabled.
When the user enters values in both fields, the form can be submitted.
However, this would generate an invalid XML document with respect to the schema since the schema specifies that a customer must also have a fullname. manages this automatically by creating an empty fullname element in the document. The generated document looks like:
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