Value equality - and null/non-null

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Value equality (a co-constraint use case)

Make the required/optional (or nillable/non-nillable?) property of a child element (or attribute?) depend on the values of one or more other elements or attributes.

source: Frank Langel [1]

(See also Value equality - and following siblings and Value equality - and children of following sibling.

Other use cases: Co-constraint Use Cases


   a validation rule such as "if field a==21 and b==32 and field x==field z
   then c must be not null"


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Possible solutions

Relax NG


Check clause


Conditional Type