Changing the form, depending on the content?

Question

PHP

Good afternoon. How to implement the appearance of additional inputs, depending on the content of the previous ones? For example: the user selects citizenship, and if he is a citizen of his country - nothing happens, but if he is a citizen of another country - 1 more input appears, in which you need to enter, for example, migration card data

Answer 1

Here is a working example
As erniesto77 wrote - listen to the change event and check the selected value, then decide what happens next.