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How to create muliselect "Dropdown List"

Accepted answer

Multi select requires the attribute to be a list attribute e.g for a list of enumerations an enumerationList (yourEnumeration).
Once you have such an attribute, create a presentation and see the presentation kind options.
https://jazz.net/library/article/1093 shows this for a stringList attribute in Lab 3,4.
Once you have such an attribute, create a presentation and see the presentation kind options.
https://jazz.net/library/article/1093 shows this for a stringList attribute in Lab 3,4.