How does Mongoose typically report a duplicate key error, and what properties can be found in the error object?

When Mongoose encounters a duplicate key error, it wraps the underlying MongoDB error. The error object caught in a `try-catch` block will typically have a `name` of `'MongoServerError'` (or sometimes `'BulkWriteError'` for bulk operations) and a `code` of `11000`. The `message` property will contain a detailed description, often including the collection name, the index that was violated, and the duplicate key value. For example, `E11000 duplicate key error collection: mydatabase.users index: username_1 dup key: { username: "testuser" }`. It might also contain `keyPattern` and `keyValue` fields detailing the index and the problematic value.