Dependable Fields

Hello,

Maybe this was asked before but I cannot find any info.

How can you create dependable fields?

An example is when you want Area > City dependencies. Meaning when choosing an area on the first select field the options (Cities) of a second field to change according to the first one.

Another approach to this is something like one select field with nested options. Something like:

-Area 1
— City 1
— City 2
— City 3
-Area 1
— City 1
— City 2

Is there any documentation how this can be achieved?

Thanks.