Which principle emphasizes that content must be presented in ways that can be perceived by all users?

The principle that emphasizes content must be presented in ways that can be perceived by all users is the pervading concept of "Perceivable." This principle is a part of the Web Content Accessibility Guidelines (WCAG), which aim to ensure that all individuals, including those with disabilities, have equal access to information and functionalities.

Under the Perceivable principle, content should be made available to the senses in multiple formats, whether it be through text, images, audio, or video. This means that information must be presented in a way that users can see or hear, and it should also accommodate various assistive technologies. For example, text should have sufficient color contrast against its background for users with visual impairments, captions should be provided for video content, and images should have descriptive alternative text for users with screen readers.

This principle is essential in creating inclusive digital environments and aligns with the broader goals of accessibility, which prioritize usability for individuals with diverse needs and abilities. By adhering to the Perceivable principle, designers and developers ensure that no user is left out due to a lack of access to content.