Enforcing fields to be filled in

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I am creating a template with several text fields. Just to be clear I am not using Base: this are fields in Writer unconnected to any database. I would like to use a macro to validate field contents (and check certain fields have been filled in) before the document is saved or exported. I have already worked out how to connect macros to the right events. But, if my macro returns False, the action (save/e-mail/whatever) still goes ahead. Is there anyway to prevent a Save from a macro event handler?