A hidden form field can be useful for saving returned id values, particularly as a means of passing them between multiple submit actions. However
Sitecore does not provide a hidden field type out of the box.
FuseIT S4S provides a hidden field type automatically, or you may have your own implementation. S4D checks to see if a hidden field is provided via the Status page under General Settings.
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If none are found, a button will be shown to Install S4D hidden field - click this to create a hidden field type in the master database under System/Settings/Forms/Field Types/Basic:
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The new field type can then be added to experience forms.as such, but this can be approximated using a Single-line text field. Simply add the hidden CSS class to the field and label under Styling:
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