From Xojo Documentation
Determines whether the left edge of the control should stay at a set distance from the left edge of the parent control, if there is one, or the owning window.
Beginning with version 2009r5, LockLeft and Locktop default to True when you add a new control to a window. Existing controls will be altered only if LockRight and/or LockBottom are not set. LockLeft has no effect unless LockRight is True.
This control can be set in the control's Inspector. The following example sets it in code.