How to check for filling fields 1s?

Question

1C

Before sending, there should be a check to see if the fields are filled in. If the fields
are not filled, then the user should receive a message about this. The message should
indicate which field is not filled in, and the error should be tied to the empty field.

Answer 1

The form attribute has properties "Fill check". Set it to Throw an error and get the required behavior.
The question is worded vaguely. I'm assuming it's about forms.