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The If-Unknown operator
?checks whether a value is unknown.
If the value is not unknown (it has a specific value), that value is returned. If it is unknown, the second value is returned.
The If-Unknown operator can be used on any WEM-type: all WEM-types can be unknown - so they also can be checked for unknown and in that case the second operand should be used. Both operands must be of the same type.
Value1if it is not unknown. Otherwise
text ? "Please enter a value"=>If `text` is unknown then the result is "please enter a value". If `text` is not unknown then `text`' is the result.
unknownnumber ? 0=> 0
unknowntext ? "some text"=> "some text"
unknownboolean ? false=> false
unknowndatetime ? Now()=> result of now() - current date and time
unknownconcept ? 'concept1'=> 'concept1'
unknownreference ? [CurrentUserRef]=> [CurrentUserRef]
"" ? 0=> expression type mismatch