sgml-validate
sgml-validate is an interactive compiled Lisp function in `sgml-mode.el
'.
(sgml-validate COMMAND)
Validate an SGML document.
Runs COMMAND, a shell command, in a separate process asynchronously
with output going to the buffer `*compilation*'.
You can then use the command C-x ` to find the next error message
and move to the line in the SGML document that caused it.