Example of rrd.meta use ?

Hello,

I'm writing a script to show disk temperature.
I read about "RRDMETA" that "(...)if you create a file called rrd.meta in the hosts rrd directory, it will lookup a legend in this file(...)". But I didn't found the information about the format and how it is used by xymon.

What is the preferred way to fill-in such rrd.meta file ?
Is there any xymon command (like status or data) to use or does it have to be edited statically ?

TIA,
	Jo