Canon EOS-1DX Af Setting Manualbook page 58

AF point expansion
(up, down, left, and right) (surrounding points)
[AF point expansion] is an [AF area
selection mode] that is best selected
when shooting sports.
For fast moving subjects that are
difficult to track with a single AF point
Shooting with AF point expansion
(up, down, left, and right)
AF point expansion (surrounding points)
Viewfinder display of [AF point expansion]. The manually
selected AF point and surrounding points lights up.
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