Описание тега cascadingdropdown
In graphical user interfaces, a typical collection of 'drop-down lists' or 'combo-boxes' which are connected in a hierarchical fashion. A well known example is a Country-State/Province-City combination.
A cascading drop-down is, in graphical user interfaces, a typical collection of 'drop-down lists' or 'combo-boxes' which are connected in a hierarchical fashion.
In a typical 3-control setup, for example, the values displayed in the third UI control depend on the selected value in the second control, whose available options in turn depend on the selected value of the first control. Whenever the first or second control changes its selected value, the dependent controls update their available options in response.
A Country / State-Province / City it is very well known example of this UI pattern.