@aws-appsync/utils Dynamodb operations don't seem to support Sets

[EHadoux]

Hello, I don't know if it's me but I'm rather confused by the whole DynamoDBOperation set of helpers in @aws-appsync/utils/dynamodb.
I need to add to a StringSet in my mutation inside a Javascript resolver.

• add documentation: Helper function to add a new attribute item when updating DynamoDB. I assume this is a SET DynamoDB operation, so not an operation on sets.
• increment documentation: Helper function to increment the existing attribute value in the item when updating DynamoDB. Which probably translates to a ADD operation despite the doc (what I need) but only accepts numbers according to the types.
• leaves use with append: Helper function to append to the existing list in DynamoDB. Looks like it's only on list.

Also, I suppose removing from a StringSet is not through decrement nor remove. Does anyone have any pointers? In the meantime I'm writing the whole thing with expression and expressionValues but that somewhat defeats the whole purpose of the library. Thanks!

PS: I could not find the source for this library, that would definitely help answer my question. Where can we find it?