The tutorial introduces the implementation of HTML cleanup and cross-site scripting (XSS) protection in real-time message streaming using the Neutrino HTML Sanitizer block and PubNub. This process involves removing potentially harmful tags from text inputs to safeguard against security threats and ensure content integrity. The tutorial demonstrates how to set up an Angular 2 web application integrated with PubNub and Neutrino APIs to effectively sanitize HTML and protect against XSS attacks. It highlights the ease of incorporating such functionality using PubNub's BLOCKS and the Neutrino API, which offers additional features like email validation, profanity filtering, and geolocation. The guide also provides a step-by-step approach to obtaining necessary API keys, integrating PubNub JavaScript SDK, and developing a user interface with Angular 2, ultimately creating a secure, real-time application environment.