Function: sgml-electric-tag-pair-mode

Toggle SGML Electric Tag Pair mode.
With a prefix argument ARG, enable the mode if ARG is positive,
and disable it otherwise. If called from Lisp, enable the mode
if ARG is omitted or nil.

SGML Electric Tag Pair mode is a buffer-local minor mode for use
with `sgml-mode' and related major modes. When enabled, editing
an opening markup tag automatically updates the closing tag.

Variable: sgml-electric-tag-pair-mode

Non-nil if Sgml-Electric-Tag-Pair mode is enabled.
Use the command `sgml-electric-tag-pair-mode' to change this variable.