[nagiosplug] developer-guidelines.sgml: Allow special value "U"

[Nagios Plugin Development]

 Module: nagiosplug
 Branch: hw/u
 Commit: 75a4ae68e476768385b483501478954e3fb4f85e
 Author: Holger Weiss <holger at zedat.fu-berlin.de>
   Date: Wed Aug 21 21:50:55 2013 +0200
    URL: http://nagiosplug.git.sf.net/git/gitweb.cgi?p=nagiosplug/nagiosplug;a=commit;h=75a4ae6

developer-guidelines.sgml: Allow special value "U"

Allow a literal "U" to be specified in place of an actual value within
the performance data string.  An "U" corresponds to RRDtool's "UNKNOWN"
value; i.e., it's meant to indicate that data acquisition failed for
some reason.  PNP4Nagios already supports this extension.

---

 doc/developer-guidelines.sgml |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/doc/developer-guidelines.sgml b/doc/developer-guidelines.sgml
index e7754f4..c10d73a 100644
--- a/doc/developer-guidelines.sgml
+++ b/doc/developer-guidelines.sgml
@@ -351,7 +351,8 @@
 		<listitem><para>min and max are not required if UOM=%</para>
 			</listitem>
 		<listitem><para>value, min and max in class [-0-9.]. Must all be the
-			same UOM</para>
+			same UOM. value may be a literal "U" instead, this would indicate that the
+			actual value couldn't be determined</para>
 			</listitem>
 		<listitem><para>warn and crit are in the range format (see 
 			<xref linkend="thresholdformat">). Must be the same UOM</para>