TClrCustomControl.CnDock Property
Gets or sets which control borders are docked to its parent control and determines how a control is resized with its parent.
published property CnDock: TDockStyle read GetDock write SetDock default TDockStyle.dsNone;
Use the CnDock property to define how a control is automatically resized as its parent control is resized. For example, setting CnDock to TDockStyle.dsLeft causes the control to align itself (changes Align property to alLeft) with the left edges of its parent control and to resize as the parent control is resized. Controls are docked in their Z-order, which is the visual layering of controls on a form along the form's Z-axis (depth).