BeginUpdate implements the BeginUpdate method of the IDockManager interface. This method is called before controls are docked or undocked. For example, TDockTree calls BeginUpdate internally from the LoadFromStream method, before docking the controls it reads from a stream. 

Once all docking or undocking is complete, the EndUpdate method is called so that the dock tree can make any final adjustments. Every call to BeginUpdate should be paired with a call to EndUpdate. BeginUpdate/EndUpdate pairs can be nested. 

EndUpdate 

LoadFromStream