Sources

S1 — MDN: Overview of HTTP

authority: official-docs
supports: Defines HTTP as a client-server protocol for fetching resources, and explains that browsers and servers communicate by exchanging requests and responses.
key-fact: "HTTP is a protocol for fetching resources such as HTML documents. It is the foundation of any data exchange on the Web and it is a client-server protocol, which means requests are initiated by the recipient, usually the Web browser."

authority: official-docs
supports: Defines the core request/response model, methods, status codes, and header fields.
key-fact: "Each message is either a request or a response. A client constructs request messages that communicate its intentions and routes those messages toward an identified origin server. A server listens for requests, parses each message received, interprets the message semantics in relation to the identified target resource, and responds to that request with one or more response messages."

authority: official-docs
supports: Describes the structure of HTTP requests and responses, including start-line, headers, and body.
key-fact: "HTTP messages are the mechanism used to exchange data between a server and a client in the HTTP protocol. There are two types of messages: requests sent by the client to trigger an action on the server, and responses, the answer that the server sends in response to a request."

authority: official-docs
supports: Defines GET as the method for retrieving a resource.
key-fact: "The GET HTTP method requests a representation of the specified resource. Requests using GET should only be used to request data and shouldn't contain a body."

authority: official-docs
supports: Defines POST as the method for submitting data to a server.
key-fact: "The POST HTTP method sends data to the server. The type of the body of the request is indicated by the Content-Type header."

authority: official-docs
supports: Defines the five classes of status codes and what each class means.
key-fact: "HTTP response status codes indicate whether a specific HTTP request has been successfully completed. Responses are grouped in five classes: Informational responses (100 – 199), Successful responses (200 – 299), Redirection messages (300 – 399), Client error responses (400 – 499), Server error responses (500 – 599)."

authority: official-docs
supports: Defines the 200 OK status code as a successful response.
key-fact: "The HTTP 200 OK successful response status code indicates that a request has succeeded. A 200 OK response is cacheable by default."

authority: official-docs
supports: Defines the 404 Not Found status code as a client error.
key-fact: "The HTTP 404 Not Found client error response status code indicates that the server cannot find the requested resource."

authority: official-docs
supports: Defines the 500 Internal Server Error status code as a server error.
key-fact: "The HTTP 500 Internal Server Error server error response status code indicates that the server encountered an unexpected condition that prevented it from fulfilling the request."

authority: official-docs
supports: Explains how to open the Network panel and inspect individual requests and responses.
key-fact: "The Network panel logs all network activity in the Network Log. Each row of the Network Log represents a resource... Click a resource to learn more information about it. The Headers tab is shown. Use this tab to inspect HTTP headers."

authority: official-docs
supports: Describes the Network panel's default columns and request details.
key-fact: "The Requests table displays the following columns by default: Name, Status, Type, Initiator, Size, and Time."