Can you explain what the letter 'O' in the SOLID principles means?

The letter 'O' in SOLID principles stands for Open/Closed Principle — the principle of openness/closure. It states that software entities (classes, modules, functions) should be open for extension but closed for modification.

This means that the behavior of a system can be extended without changing existing code, which helps avoid errors and simplifies maintenance. For example, when adding new functionality, it is better to create new classes or methods rather than changing old ones.

In Flutter, this is important for creating extendable and maintainable widgets and components.