Why can't I import a .sdltm into another .sdltm?

Question

I have a Big Mama legal TM open in Studio, and I want to import the content of another .sdltm on my computer. I tried Import (which would seem the most logical way to do this), but am not allowed to select .sdltm files? What am I missing here? 
 Michael

Paul · Answer

A TMX doesn't contain all the properties of a TM. It only contains those fields & attributes that were actually used for the data held in the TMX. So to effectively merge two SDLTMs together the merge route is preferable. It's also very good if you have different TMs in different languages or if you want to change the way the leverage is affected for different filetypes. 
 
But I agree... the UI here is not intuitive at all.

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Why can't I import a .sdltm into another .sdltm?