8.21 WCAG 2.1 Success Criterion 3.2.1 − On Focus

When an item on a webpage receives focus, such as by using the Tab key in the keyboard, ensure it does not change the context. For example, by displaying a dialogue box when a person tabs to a field.

Before Rectification

In this example, a field receives focus, and a help dialogue box describing the field and providing options opens. As a keyboard user tabs through the webpage, the dialogue opens, moving the keyboard focus away from the control every time the user attempts to tab past the field.

After Rectification

Instead, the webpage should allow the user to activate "Help" only at their choice rather than forcing them to read "Help" with each tabbed field.

WCAG 2.1 Reference:

https://www.w3.org/WAI/WCAG21/Understanding/on-focus