How can I set 1Password to fill an arbitrary field with a saved value?

Hey @franklaw, 1Password does have the ability to save and fill non-login fields. In some cases, 1Password will save these details automatically. In some cases, you will have to create a custom field in order to add these details to your login.

Please note that while it is possible to create a custom field in the item to hold your info, we can't guarantee that it will fill. The success of filling the custom field is largely dependent on how the form in question is coded. The example you gave unfortunately doesn't provide us enough information to give you a specific answer. Do you have a link to a live form on which an issue like this appears? If so, please let us know.