I have a form that is split into two parts,
The one half of the form is required. The other half of the form is only required if any field on the form is partially filled in.
For the form fields that are always required, I have a little red star next to them.
What is a good way to indicate to the user that the other fields are only required if one or more of them is filled in?
(My first instinct is to not even place an indicator at all, and have the validation messages appear, but I'm not really sure if that is clear enough).
Fade the red stars in when they start typing in one of the trigger fields.
Why not use the disabled attribute on the form fields in the second part of the form, or otherwise grey them out with CSS with some kind of partial overlay, then use the change event of any of the fields in the first part of the form to undisable/remove the overlay?
Have you considered making a form wizard of some sort? That way if more information is required, it sends them to the next part of the form. If not, then it just submits the form.