Suggested file extension for tar lzip

[Joel May]

Hello,

I'm working on adding lzip support to Duplicati in the form of .tar.lz files.  
I need to shorten the file extension down to a single segment.  Is there an 
official recommendation for what that file extension should be?  Following 
convention set by other formats (e.g. tgz, txz), it would be tlz.  Some places 
on the internet (i.e. Wikipedia) list tlz as "plain" tar LZMA, so that could 
cause confusion.

--Joel May

Cite: https://en.wikipedia.org/wiki/7z#Limitations
Cite: 
https://en.wikipedia.org/wiki/List_of_archive_formats#Archiving_and_compression