Question about PmPose in posemath.h

["Eding, Bert" <b.eding-at-Nyquist.com>]

I guess this question is for a Fred to answer.
Lately I am diving, at least trying to, in Kinematics.
My question is about the definition of the PmPose structure, it is defined
as:

typedef struct
{
  PmCartesian tran;
  PmQuaternion rot;

} PmPose;

while PmQuaternion and PmCartesian are defined as:

typedef struct
{
  double s, x, y, z;

} PmQuaternion;

typedef struct
{
  double x, y, z;

} PmCartesian;


My question 1):
Is the order of rotations defined by the "s" value or how is this done?

I expect that the PmPose is entended to unique define a robots position,
I have an understanding problem with the definition of the rotation.
It is clear that the order of rotation is important, 
rotate x, then y is different from rotating y and then x.

The reason that I ask is that in another mathe library that I have the pose
is
defined as:

typedef struct 
{ 
	VECTOR pos; 
	ORI ori; 
} POSE;

Here VECTOR is the same as PmCartesian, but ORI is defined as:
typedef struct 
{ 
	double e[3][3]; 
} ORI;

Here ORI is the rotation matrix, here I understand that the 
POSE structure does unique define the robots position, I do not understand
this
with the PmPose from the RCS-lib.


My question 2):
How can I convert from the PmQuaternion to a rotation matrix?

Thanks in advance
Bert Eding