请问initialization里的代码什么时候被调用

我有个单元文件uses了controls,
controlsinitialization里的代码:
  NewStyleControls := Lo(GetVersion) >= 4;
  InitControls;
  StartClassGroup(TControl);
  ActivateClassGroup(TControl);
  GroupDescendentsWith(TCustomImageList, TControl);
  GroupDescendentsWith(TContainedAction, TControl);
  GroupDescendentsWith(TCustomActionList, TControl);
请问这些代码什么时候被调用