Where can I find a reference document about the SDLXLIFF format?

Hi

Can someone tell me where I can find a reference document that explains the meaning of the various elements of the SDLXLIFF format?

I need this to understand the content of an SDLXLIFF file and to be able to make minor changes to it.

My searches in Producthelp, KB and Community have so far been unsucessful. I am sure this information must be available (at least to developers).

Thanks for any hint.

Walter