How to research about DBus to trigger Suspend mode?

[c.buhtz at posteo.jp]

Hello,

the question is less about how to trigger Suspend mode via DBus. It is 
more about how to answer such questions myself.

I often stumble across DBus. I find a lot of examples and all this fancy 
"org.freedesktop"-like strings for methods/objects/services related to 
DBus.

But how do I know which one to use? Is there a catalog somewhere? Is 
there a logical system behind it I have not understood yet?
And how can I be sure that the used name-string is persistent on all GNU 
Linux distros and their desktop environments?

Thanks,
Christian