Install from editors/emacs or editors/xemacs.

Edit ~/.emacs, adding these lines:

    (defun local-sgml-mode-hook
      (setq fill-column 70
	    indent-tabs-mode nil
	    next-line-add-newlines nil
	    standard-indent 4
	    sgml-indent-data t)
      (auto-fill-mode t)
      (setq sgml-catalog-files '("/usr/local/share/xml/catalog")))
    (add-hook 'psgml-mode-hook
      '(lambda () (local-psgml-mode-hook)))