Read this question carefully since we are asking about things we want to avoid. HTML5 should **NOT**...

HTML5 should not be used for the following purposes:

1. Security-sensitive applications: HTML5 is not suitable for building applications that require high levels of security, such as online banking or payment systems. It lacks the necessary security features and controls to protect sensitive user data.

2. Real-time applications: HTML5 is not well-suited for building real-time applications that require instant updates and low latency, such as multiplayer games or live chat applications. Other technologies like WebSockets or WebRTC are better suited for these types of applications.

3. Complex animations and graphics: While HTML5 does support basic animations and graphics, it is not ideal for creating complex and high-performance animations or graphics. For more advanced animations and graphics, technologies like CSS3 or WebGL are more suitable.

4. Cross-platform mobile app development: Although HTML5 offers the advantage of cross-platform compatibility, it may not provide the same level of performance and native functionality as native mobile app development. For resource-intensive mobile applications, native development using technologies like Swift for iOS or Java for Android is recommended.

5. Offline capabilities: HTML5 does provide some offline capabilities through technologies like the Application Cache and Local Storage. However, if your application requires extensive offline functionality, a native or hybrid mobile app development approach may be more appropriate.

It is important to carefully consider the specific requirements of your project before deciding to use HTML5, as it may not be the best choice for certain scenarios.