What does the yellow star behind units mean?

[Ariminio]

Excuse me if this is a weak question, but what does the yellow star behind units mean? And is it a new feature? I never noticed it before.

 

[Iceciro]

Its the level the units will start at (from bonus XP).

It is a new feature, as is tracking all the xp producing buildings below the units.

 

[Ariminio]

Oh that is a great feature, thank you for the explanation.