@findex sgml-validate
Run a shell command (which you must specify) to validate the current
buffer as SGML (@code{sgml-validate}).
-@end table
@item C-x TAB
@kindex C-c TAB @r{(SGML mode)}
@findex sgml-tags-invisible
Toggle the visibility of existing tags in the buffer. This can be
used as a cheap preview.
+@end table
@vindex sgml-xml-mode
SGML mode and HTML mode support XML also. In XML, every opening tag