The perceivable principle is the first principle and it states that the information on a user interface component must be presentable to users in such a way that they can perceive. The principle one gives more importance on the perceivable aspect of the presentation. This principle specifies four aspects: They are as follows:
- Text Alternatives: Provide text alternatives for any non-text content so that it can be changed into other forms people need, such as large print, braille, speech, symbols or simpler language.
- Time-based Media: Provide alternatives for time-based media.
- Adaptable: Create content that can be presented in different ways (for example simpler layout) without losing information or structure.
- Distinguishable: Make it easier for users to see and hear content including separating foreground from background.
- Operable – User interface components and navigation must be operable.
The second principle is on the operable nature of the content. The operable principle speaks on four aspects. They are mentioned below.
- Keyboard Accessible: Make all functionality available from a keyboard.
- Enough Time: Provide users enough time to read and use content.
- Seizures: Do not design content in a way that is known to cause seizures.
- Navigable: Provide ways to help users navigate, find content, and determine where they are.
The Third principle speaks on the understandability of the content. It is stated that the Information and the operation of user interface must be understandable. The understandable principle speaks about three aspects.
- Readable: Make text content readable and understandable.
- Predictable: Make Web pages appear and operate in predictable ways.
- Input Assistance: Help users avoid and correct mistakes.
This is the fourth principle in the WCAG 2.0 recommendation. This principle states that the content must be robust enough that it can be interpreted reliably by a wide variety of user agents, including assistive technologies. The robust principle has only one aspect.
- Compatible: Maximize compatibility with current and future user agents, including assistive technologies.
Developing the web contents so as to meet the guidelines specified in the WCAG2.0 makes the content accessible to more audience.