On some keyboards, the "ab" button switches on and off the Input Method Editor (IME). The IME helps writing words faster by proposing auto-completed words based on your input.
When IME is on, your input is highlighted in blue, and pressing on your computer keyboard:
- "Escape" cancels the ime action and lets your input unchanged,
- "Enter" or "space" replaces your input by the proposition #1 or by your input if there is no proposition,
- "1", "2", "3", ... replaces your input by the proposition #1, #2, #3, ...