Cypress Tests : parent / child / dual commands

There are three kinds of commands:
```
// -- This is a parent command --
// Cypress.Commands.add("login", (email, password) => { ... })
//
//
// -- This is a child command --
// Cypress.Commands.add("drag", { prevSubject: 'element'}, (subject, options) => { ... })
//
//
// -- This is a dual command --
// Cypress.Commands.add("dismiss", { prevSubject: 'optional'}, (subject, options) => { ... })
```
Mention these.

The issue names no file, test, or documentation entry point, so first locate the section covering Cypress commands in the TypeScript book. Compare its coverage with the supplied parent, child, and dual command examples; done means all three command kinds are mentioned accurately.

Written by the indexing model from the issue text.