Let's populate an HTML5 DataList with countries via Knockout.js. The result will be as shown below, that is, you will have code completion via your DataList...
...and, when a country is selected, and focus moves out of the DataList (e.g., use the Tab key), its states will be displayed in an unordered list below:
The completed sample code is here:
Now that we have countries and states, let's create a DataList and populate it and, when a country is selected, list its states:
Line 26 above was definitely the trickiest to figure out, where this provided the missing piece of information.