Typo3 8: “save and preview” backend button for custom model

It’s kinda easy:

TCEMAIN.preview {
        tx_ophi_domain_model_entry {
                # Available with latest 8.7+ only
                useCacheHash = 1
                previewPageId = 22
                useDefaultLanguageRecord = 0
                fieldToParameterMap {
                        uid = tx_ophi_entry[entry]
                }
                additionalGetParameters {
                        tx_ophi_entry.controller = Entry
                        tx_ophi_entry.action = show
                }
        }
}