From Xojo Documentation

Property (As Boolean )
aDesktopContainer.LockLeft = newBooleanValue
BooleanValue = aDesktopContainer.LockLeft

New in 2021r3

Supported for all project types and targets.

Determines whether the left edge of the DesktopContainer should stay at a set distance from the left edge of the parent control, if there is one, or the owning DesktopWindow.

See Also

UserGuide:Desktop Control Hierarchy