How to create a Custom Datatype for Content Fragment Model?
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Looks like you have a pre-defined set of data types. Content Fragment Models
HOwever - If you want to build custom models for AEM components - you should look at perhaps at using HTL and Sling Models where you have more more power of creating custom models to meet your business requirements.
Take a look at how the CARD component is built using the WEEKEND tutorial (part 6) -