Adding MathML entities?

Hi

I am interested in adding some MathML entities to my copy of Amaya 5.1
(e.g. things like U+2124 ℤ U+2102 ℂ U+211D, ℝ 
etc  which I use often).

Can someone point me in the right direction.  Is there any documentation
on how this is done? I grepped through the code but couldn't see where
the characteristics (e.g. what they look like) for entities were
defined.  

Thanks, 
regards 
  Robert Valkenburg