Fox output can be previewed by adding a 'Preview' button to the form, plus a (:foxpreview:) markup to display the preview:

(:input submit preview 'Preview':)
Add a submit button with exact name preview and button label 'Preview' (substitute text of your choice).
(:foxpreview:) or (:foxdisplay:)
Add directive at the place in the page where you would like the preview to be shown.
(:if foxpreview:)
Optional - conditional markup to show text only when 'Preview' is clicked.
(:foxpreviewtemplate "...":)
Optional - Alternative template markup used for the preview instead of the standard (:foxtemplate "....":) or other template page.
Optional - Alternative template parameter used for preview instead of template=... parameter.

Fox is also specially configured to work in conjunction with FoxEdit links, so FoxEdit forms can use a 'Preview' button.

To include the group header in the preview, specify this in the foxpreviewtemplate: (:include {*$Group}.GroupHeader :)