(defun my-tagger (tag)
(interactive "sTag: ")
(if (not (use-region-p))
(error "no region is highlighted")
(let ((text (buffer-substring (region-beginning) (region-end))))
(delete-region (region-beginning) (region-end))
(insert (format "<%s>%s</%s>" tag text tag)))))
(global-set-key (kbd "<f7>") 'my-tagger)