Storing multiple entries to a Keyword field from a form

Has anyone tried storing multiple entries to a Keyword field from a form? There does not seem to be a way to do that. The index fields from the document on the left of the Indexing page in the Form Designer are only listed once so there seems to be no way to point to several different entries from the form for that field.

Any clues appreciated,

Steve
Use CHECKBOX type field on the form and associate the field output with a keyword field in your File Cabinet. This way, multiple checkbox selections on the form will be populated into the keyword field.

The Checkbox method works if the text results of the checkboxes are the same text desired in the keyword field but this does not allow for free-fom text input. For example, if the checkbox is for 'Model' and allows A, B, C and D, one can choose any of those and they map to the keyword field. We need to capture  multiple names from a form, such as the names of family members traveling together.  Could this be accomplished?