Works in any mode.
The exception here is that if the camera is using the "AI Servo" focus mode then the camera will continuously attempt to track focus for moving subjects. In such a situation the focus wont "lock" but that's because you've asked to the focus system to continuously track and update focus on your selected AF point.
Another option is to enable back-button focus. This removes the focus feature from the shutter button and moves it to a button on the back (on the T3 I believe it uses the asterisk [*] button.) When you enable this feature, the camera will ONLY adjust focus when you press that button.
There are some YouTube videos explaining how to enable this mode (it is a custom function).
Many sports photographers like that mode because they can track an athlete running down the field while they continually hold the back-button to maintain focus. However... if they see someone about to pop in front of the camera and they do not want the camera to re-focus on the distraction walking in front of the camera... all they have to do is release the back-button while they wait for them to pass by ... then resume focus on their athlete by pressing the button again. Typically in that short amount of time the athelete will not have moved far enough to fall out of the depth of field.
I have a Canon 1100D.
I would like to know if 'focus lock' is possible in all modes of exposure of this model, whether in Basic zone or in Creative zone.
Focus lock = In Focus, basic distance focus of a stationary subject.
Focus track = Adjusting Focus to Track Subject. Tired of trying to get your toddler, or running back, to stand still for a photo? Use focus track.
You'll always be able to get focus lock.