Which combination is essential for ensuring web accessibility?

Ensuring web accessibility fundamentally revolves around the interaction between content, browsers, and users' experiences. Content must be designed and structured in a way that is inherently accessible, using semantic markup and appropriate alt text for images, for instance. This ensures that assistive technologies can interpret and present the content correctly to users with disabilities.

Browsers play a crucial role, as they are the mediums through which users interact with web content. Different browsers may behave differently when rendering web pages, and ensuring that your website is compatible across various platforms is vital for accessibility.

Finally, users' experiences encompass a variety of individual needs and preferences. Users come with different abilities, such as visual impairments, cognitive disabilities, or motor impairments, and their experiences with web content can vary widely based on how well that content is accessible. Understanding these diverse experiences and designing content that is usable for everyone forms the crux of effective web accessibility.

The other options focus on more specific elements that, while important for overall web development, do not comprehensively cover the broader aspects of accessibility in the same way that content, browsers, and user experiences do.