[texhax] implementation of x' in math

[Alexandru Scorpan]

How is the translation of $x'$ into $x^{\prime}$ implemented?

I am asking for three reasons:
1. I would like to change it to a different version of the prime 
symbol, without messing with \prime;
2. I would also like to implement that $x''$ be interpreted as 
$x^{\second}$, where \second is a better kerned version of two 
\prime's;
3. I am just damn curious.

-- Alex