When creating a form, an index is automatically assigned to the control fields that are added to this form; every control field added is assigned an index increased by 1. If you change the index of a control, the indices of the other controls are updated automatically. Elements that cannot be focussed (Tabstop = No) are also assigned a value. However, these controls are skipped when using the Tab key.
当创建一个窗体时，插入到窗体中的控件字段会被自动分配索引，每增加一个控件字段，索引会自动加 1 并分配给新增加的控件字段。如果修改一个控件字段的索引，其他控件字段的索引会自动更新。不能获得焦点的元素 (Tabstop = No) 也会被分配一个索引。但是在按 Tab 键时这些控件字段会被跳过。