Hereditary trait

[Suva Mail]

"The heir disposes of one hereditary trait which is exclusive to him and no one else can acquire it."

Sorry I tried it in the game and read it from start to end and form end to start and I still don't get what does it mean?
I understand that one (or more?) emperor skill can be given to hes heir (only first born son??) or what.
Who ever I have ever appointed to heir, there was not a one skill that was given forward to heir or I really don't understand what that sentence means.

[Suva Mail]

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