How to declare a non-string element as having optional content in XML Schema?

You need xs:element name="start-at" minOccurs="0 mixed-mode isn't relevant to your situation, you don't need that. By default minOccurs="1 i.e. The element is mandatory With minOccurs="0", you either specify the element with content, or not at all.

If you want to be able to permit start-at then you cannot use xs:dateTime.

You need mixed-mode isn't relevant to your situation, you don't need that. By default, minOccurs="1", i.e. The element is mandatory.

With minOccurs="0", you either specify the element with content, or not at all. If you want to be able to permit , then you cannot use xs:dateTime.

You can define your own types as union of types. 1/ define the "empty" type as a string that only allows "" ähm nothing :) 2/ next define a type that allows date AND empty 3/ declare all your nullable datetime elements as type="empty-dateTime.

Thank you 'robbie', your solution worked well for me, that is, the 'empty-dateTime' strategy which I adapted to a 'optionalDecimal' type like so: Here you can have an element that can be empty or contain a decimal value. :).

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