A "Public" API is typically exposed to external developers and allows them to extend the functionality of a platform or application. It's accessible to external parties for integration.

By implementing caching, an API can efficiently handle multiple requests without degrading performance. Caching involves storing and reusing frequently requested data, reducing the need for repeated processing and resource-intensive operations, thus enhancing API efficiency.

GraphQL effectively handles under-fetching and over-fetching of data by allowing clients to specify exactly what data they need, eliminating the need to make multiple requests for related data and minimizing unnecessary data transfer. This results in more efficient data retrieval.

The choice between a Public, Private, or Partner API significantly impacts the security of a web application. Public APIs expose data and services to anyone, potentially increasing security risks and requiring robust authentication and authorization. Private APIs offer the most security as they limit access to authorized users only. Partner APIs strike a balance between public and private, allowing controlled access to selected partners. The security level depends on the implementation of the API and the measures taken to protect it.

The primary concern when considering API security is data privacy and encryption. APIs often transmit sensitive data, and it's crucial to protect this data from unauthorized access and interception. Encryption ensures that data remains confidential and secure during transmission.

A "Private" API is restricted to specific partners or collaborators and may require additional authentication mechanisms to access. These APIs are not open to the public and are designed for controlled access by trusted entities.

In SOAP, error handling is typically done using standard XML fault elements, making it more structured and explicit. In contrast, REST often uses descriptive error messages in the response body, providing more flexibility but potentially making error interpretation less standardized. Understanding these differences is crucial when choosing between the two.

When implementing Role-Based Access Control (RBAC) in APIs, authorization is crucial to ensure that only authorized individuals have access to specific data. Authorization defines what actions and data a user or system is allowed to access. It is a key component of RBAC, ensuring that users are granted appropriate permissions and roles to perform their tasks while maintaining data security and integrity.

One of the benefits of using OpenID Connect is that it can help in eliminating the need for password storage. OpenID Connect allows for secure authentication without the application having to store user passwords. It achieves this by enabling Single Sign-On (SSO) and delegating the authentication process to an Identity Provider (IdP), reducing the security risks associated with password storage.

Comprehensive API documentation for a RESTful API should include sections on API endpoints, detailing all available endpoints with their URLs, request/response formats, and usage examples. Authentication details, including how to authenticate, obtain API keys or tokens, and code samples, should be provided. Rate limiting information, error codes, and explanations should be included. Additionally, a historical changelog with API changes and versioning information can be helpful for developers.