3.2.1 On Focus
Make Web pages appear and operate in predictable ways.

About

When a user inters information or uses Tab key in the keyboard, ensure it does not change the context of the webpage such as by displaying a dialogue box when a person tabs to a field.

Example:

Before Rectification

image  of displaying a dialogue  box when a person tabs to a field.

When the “Password” field received focus , the Help dialogue box will display automatically. This affect focus of users who rely on using keyboard only.

After Rectification

image  of not displaying a dialogue  box when a person tabs to a field.

Now, “Help” dialogue box will not be displayed automatically, user will have the control to make it displays or not.