Without @orient:

v@N; // +Z axis of the copy
v@up; // +Y axis of the copy

Not ambiguous @orient, thanks to Matt Estela!

matrix3 m = maketransform(@N,@up);
@orient = quaternion(m);

Representing a quaternion from an angle and axis. The angle is specified in radians:

float angle = radians(90);
vector axis = set(0, 1, 0);
p@rot = quaternion(angle, axis);

Representing a quaternion from a 3×3 rotational matrix:

float angle = radians(90);
vector axis = {0,1,0};
matrix3 m = ident();
rotate(m, angle, axis);
@orient = quaternion(m);

PI eight digits

#include "math.h";
float e = M_E; //2.7182818
f@angle = PI; //3.1415926
f@angle = radians(180);

Quaternion to Euler rotations
thanks to DJ

vector  qToE(vector4 q_value){
    float   q_0 = q_value.w ; 
    float   q_1 = q_value.x ; 
    float   q_2 = q_value.y ; 
    float   q_3 = q_value.z ; 
    vector  out = {0,0,0} ; 
            out.x = degrees(atan2(2*(q_0*q_1+q_2*q_3), (1-2*(q_1*q_1+q_2*q_2)))) ; 
            out.y = degrees(asin(2*(q_0*q_2-q_3*q_1))) ;
            out.z = degrees(atan2(2*(q_0*q_3+q_1*q_2), (1-2*(q_2*q_2+q_3*q_3)))) ;
    return out ; 
}

v@ro = qToE(p@orient);