Canon EOS 700D Instruction Manual page 99

AI Focus AF for Automatic Switching of AF Operation
AI Focus AF switches the AF operation from One-Shot AF to AI
Servo AF automatically if a still subject starts moving.
After the subject is focused in One-Shot AF operation, if the subject
starts moving, the camera will detect the movement, change the AF
operation automatically to AI Servo AF, and keep tracking the
moving subject.
When focus is achieved with AI Focus AF with the Servo operation active,
the beeper will continue beeping softly. However, the focus confirmation
light <o> in the viewfinder will not light up. Note that focus will not be
locked in this case.
f: Changing the Autofocus OperationN
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