Perhaps AWS Comprehend's documentation has changed after my last knowledge update in January 2022. But in the past, there may have been a number of reasons why there wasn't thorough documentation available regarding the file structure of the Comprehend custom document classification training data:

Custom document classifiers can be trained on a variety of document types and formats using Understand's flexibility and customization features. Giving file structure documentation that is universally applicable may be difficult due to the flexibility.

Service Evolution:

Continuous updates and enhancements are made to AWS services. At some point during the service's development, perhaps when improving core functionality took precedence over detailed documentation, this may have been the case.

Utilization-Specific Use Cases:

Different industries and use cases may require quite different approaches to document classification. Users could possess differing