Is there Salesforce documentation on RestResource Object?

Question

I'm following a design pattern set by one of our devs.

    RestResource.RequestBody requestBody = RestResource.getRequestBody();

I'm trying to find documentation on this object, but I can't seem to find it anywhere. Is this design pattern outdated?

Should we be using something like RestContext instead?

Apex class

@RestResource(urlMapping='/endpoint')
global without sharing class myRestClass {
    @HttpPost
    global static void create() {

        RestResource.RequestBody requestBody = RestResource.getRequestBody();
        //Call your caller class

        System.debug(requestBody.body);
        myProcessingClass mp = new myProcessingClass(requestBody.body);

        //Check response
        System.debug('trying to process');
        mp.processActivity();

        RestResource.getResponse('SUCCESS', 201);


    }
}