ManagedObject.extend third optional parameter "FNMetaImpl?"

In the ManagedObject "extend" function documentation you can see that it is possible to use the third parameter for specifying a Constructor function for the metadata object.

Since in TS you don't call directly the "extend" function but rather the builder/transpiler does it, how can one pass a custom metadata costructor to the definition of a custom class?

Since metadata information (that are part of the second parameter "oClassInfo?" in the "extend" call) are automagically passed by defining a "public static metadata" (or "static readonly metadata", not very clear) attribute in the class (and doesn't always work...) , I suspect that there mey be something along the same line, like defining a static "metadataImplementation" or similar?

Is there an alternative way to define and use a custom metadata constructor for my custom class?

Thanks

Start with the ManagedObject.extend documentation and the TypeScript builder/transpiler path that handles the class definition. Trace how the second-parameter metadata is represented and whether the third FNMetaImpl parameter is exposed. Done means establishing and documenting a supported way to provide a custom metadata constructor, or clarifying that none exists.