add note on variable names

git-svn-id: svn://svn.oetiker.ch/rrdtool/branches/1.2@599 a5681a0c-68f1-0310-ab6d-d61299d08faa

diff --git a/program/doc/rrdgraph_data.pod b/program/doc/rrdgraph_data.pod
index e8b2c6719d3ecebb658bc0bd72c059b9745d2f7d..c57b2c356d04c35527d7a8ffe4160c0f2c4e3fec 100644 (file)
--- a/program/doc/rrdgraph_data.pod
+++ b/program/doc/rrdgraph_data.pod
@@ -19,6 +19,9 @@ useful information such as maximum, minimum etcetera. Two of the
 instructions use a language called B<RPN> which is described in its
 own manual page.
 
+Variable names (I<vname>) must be made up strings of the following characters
+C<A-Z, a-z, 0-9, -,_> with a maximum length of 255 characters.
+
 =head1 DEF
 
 B<DEF:>I<E<lt>vnameE<gt>>=I<E<lt>rrdfileE<gt>>:I<E<lt>ds-nameE<gt>>:I<E<lt>CFE<gt>>[:step=I<E<lt>stepE<gt>>][:start=I<E<lt>timeE<gt>>][:end=I<E<lt>timeE<gt>>][:reduce=I<E<lt>B<CF>E<gt>>]