/*********** "BNF"-expression syntax ************/
/*
E::= E xor A !! E or A !! A
A::= A and N !! N
N::= not N !! R
R::= P eq P !! P lt P !! P le P !! P gt P !! P ge P !! P ne P !! P
P::= P + T !! P - T !! T
T::= T * M !! T / M !! T mod M !! T shl M !! T shr M !! M
M::= - M !! + M !! S
S::= <over>: F !! F
F::= F ptr B !! seg B !! offset B !! type B !!
     length B !! last B !! B
B::= ( E ) !! [ bracket-expression ] !! I
I::= varaible !! . number !! number !! label !! string
<over>::= segment register
(stringlength < 3)

*/