ASP.NET Core Web APIs primarily use the JSON (JavaScript Object Notation) format for transmitting data. JSON is lightweight, human-readable, and widely supported, making it a popular choice for APIs.

To configure session timeout in ASP.NET Core, you should use the "app.UseSession" method in the "Configure" method of the Startup.cs file. The session timeout can be set using the "IdleTimeout" property in the services.Configure method. This middleware enables session state in the application, and configuring the timeout here is the correct approach.

In an ASP.NET Core project, the "Program.cs" file serves as the entry point of the application. It contains the Main method, which creates the web host and starts the application. This is where the application configuration and host building occur before the application starts listening for incoming requests.

Attribute routing in ASP.NET Core allows for centralized route configuration, making it easier to define routes for specific actions or controllers directly within the code using attributes. This provides a more intuitive way to specify routes and helps keep routing logic within the controllers where it belongs.

The primary distinction between Visual Studio and Visual Studio Code is that Visual Studio is a full-featured integrated development environment (IDE) with a wide range of features for various types of development, whereas Visual Studio Code is a lightweight, open-source code editor with extensibility for customizing and configuring it according to the developer's needs.

In the context of ASP.NET Core, "lightweight" refers to reduced memory usage and a small download size. ASP.NET Core is designed to use fewer system resources, making it efficient for hosting applications and reducing operational costs. This lightweight nature also allows faster startup times for applications.

In an ASP.NET Core MVC application, the configuration for routes is primarily done in the Startup.cs file. In the Configure method, developers define route patterns and specify which controller and action should handle incoming requests, enabling the routing system to map URLs to controller actions.

To restrict certain parts of your application to specific subdomains using attribute routing, you can utilize Route Constraints. By defining constraints on route parameters like {subdomain}, you can ensure that certain routes are accessible only when the subdomain matches the required value, fulfilling the client's requirement for subdomain-based access control.

Azure Kubernetes Service (AKS) is tailored for deploying Docker containers. It's a managed Kubernetes container orchestration service that simplifies deploying, managing, and scaling containerized applications using Kubernetes.

Tag Helpers are processed in the order determined by the Order property. By setting the Order property, you can control the sequence in which multiple tag helpers are applied to an HTML element. This is crucial for scenarios where you need precise control over tag helper execution.