What are the requirements for key items?

A key item must:

A key item must not:

Be a hidden item or be attached to a read-only control.
Be a child in a compound item.
Be a child of a conditional item.
Have a combination of composite keys and individually unique keys in the same repeating form or section.
Have a conditional child that is a compound item or is formatted as a checkbox or radio control.
Be formatted as a checkbox.
Have a caption that is aligned at the top or bottom of the control, including captions for conditional items.
Be in a nested control structure, unless it is at the top of the hierarchy and conforms to other eligibility requirements.
Be in a repeating section, if the key is for a repeating form.