bug#13859: 24.3.50; Non-interactive, single shot validation of XML against rnc files

[Jambunathan K]

Is there an API I can call for Non-interactive, single shot validation
of XML against rnc files.

nxml-mode has commands for *interactively* validating XML files against
rnc spec.  It seems that C-c C-n with `rng-validate-mode' on is more
geared toward interactive use - i.e., I see references to timer,
validating only a fraction/chunk of the XML at a time, use of overlays
etc.

Is there a way to validate against a rnc file in a *non-interactive* and
*single-shot* way?  A simple defun that visits an XML file and reports
"file is well-formed" or "file is malformed with first error at this
position" would be good.  (Desirable: Provide "grep-like" compilation
errors for XML files.)

Context: Org mode has HTML and ODT exporters.  It will be nice to
passthrough the exported files to a validator for automatic catching of
errors.

In GNU Emacs 24.3.50.10 (i686-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2013-03-03 on debian-6.05
Bzr revision: 111916 eggert@cs.ucla.edu-20130302183934-3d4pouz6i3qwkxs9
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
System Description:     Debian GNU/Linux 6.0.5 (squeeze)

Important settings:
  value of $LANG: en_IN
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: iso-latin-1-unix
  default enable-multibyte-characters: t