How to make UI fields created in htm page mandatory

Hi,

I understand that the UI fields which are populated at Context Node level, can be made mandatory in Configuration tab.

But I have a scenario in component/view: GSMCDDLB/DropDownList, there are dropdown fields like Category1,Category2,......Category10.

These fields are created at htm page of the controller class using <thtmlb:dropdownListBox />. And this view does not have configuration tab . So my query is how do we make these dropdown fields to be mandatory to be selected. So basically, while I am saving the Interaction Record, it should give an error to fill these dropdown fields by selecting any value.

This component GSMCDDLB exists in Interaction Record page under "Categorisation" tab.

To summarise, my queries are:

1)  How to make fields created in htm page mandatory?

2)  Interaction record should not be saved when these fields are not filled. How do we do it.