2.1.1 Keyboard: All functionality of the content is operable through a keyboard interface without requiring specific timings for individual keystrokes, except where the underlying function requires input that depends on the path of the user’s movement and not just the endpoints. (Level A)
Note 1: This exception relates to the underlying function, not the input technique. For example, if using handwriting to enter text, the input technique (handwriting) requires path-dependent input but the underlying function (text input) does not.
Note 2: This does not forbid and should not discourage providing mouse input or other input methods in addition to keyboard operation.
This success criterion requires that all functionalities must be accessible and operable to users using a keyboard. Normally users with disabilities & elderly people depend a lot on keyboard to navigate to all parts of the web page & if any part of the web page is not operable with keyboard then it fails this check point. People generally use tab to move forward, shift+tab to move backward & screen reader users use arrow keys a lot to navigate. This success criterion addresses the needs of people with motor disabilities, visually challenged users & elderly users.