Mathematica: Webel: ADT pseudo classes: POLICY: The expression '$$' is reserved as the primary named parameter for the defining pattern of all ADT classes that extend the universal base 'ADT' class.

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ADT$Map /: get[$$_Association] := $$;

In the Webel recipe for ADTs this is actually inherited from a base ADT and uses a template 'pattern' variable that is passed to a definer function:

ADT /: get[pattern] := $$;

So in the above case pattern would be $$_Associaton.

This policy offers a clearly identified variable expression that is not likely to otherwise be used in code (unless deliberately) and helps avoid this possible clash:

However, to make the Webel ADT recipe work when referenced from OTHER packages, you need this:

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